I'm truly at a loss here, please help (cycling low KH tank)

[Seisage]

Apologies for the long post ahead. Alright, so, I'm currently working on constructing an Ucayali River biotope. I just set up the tank yesterday and I'm really at a loss for how to cycle it.

My tap water's KH (and GH) is naturally extremely low, at around 35ppm (~2 degrees). The tank's pH is currently at 6.8, although my tap water is ~7.2. These parameters are near perfect for a blackwater tank, and that is exactly what I'm shooting for, as many parts of the Ucayali are soft, acidic, and tannin stained. Now, the problem is, of course, that traditional nitrogen cycling requires higher KH and ideally a higher pH. Many sources I've found recommend simply adding a source of KH to raise it. I really don't want to have to do this, as it would require constant maintenance to keep KH levels up long-term and I'd worry about how bringing the KH back down later would affect the bacterial colony. However, basically all sources say that traditional cycling simply isn't possible with KH below 50ppm.

Researching blackwater tank cycling or low KH cycling in general unfortunately hasn't been very helpful. I've found a lot of conflicting or otherwise unhelpful information. Many people recommend maintaining KH with regular additions of tap water, which... will not help in my case with my ridiculously soft water. Or, people recommend converting an existing tank to a blackwater one, but that requires having a cycled, mature tank to convert. Other people say don't even bother trying to cycle since the low pH means ammonia is non-toxic anyway. If possible, I'd like to avoid making that gamble and potentially losing fish because of it... There's nitrite to worry about too, anyway.

Now, I hear that the set of nitrogen-processing organisms in blackwater conditions is completely different than the typical players. Different bacteria, archaea, etc. How do I go about growing them? I imagine I should probably add leaf litter and botanicals now to get to a stable pH before trying any sort of cycling process, correct? Once pH is stable, what steps should I take to make sure the tank can handle fish bioload? How long does it usually take for the bacteria/archaea colonies to grow? I hear it takes at least a few months. Is it possible to add any fish at all before then, or do I just need to be patient and wait it out? If at all possible, I would appreciate somewhat direct instructions. Vague answers just leave me with more questions... If no instructions are possible, then so be it, I suppose.
FYI: I am aware of the recent blackwater cycling thread here, but it's ultimately more about maintaining a blackwater tank rather than setting one up.

Context which is likely important:

• The tank is planted with frogbit and hopefully soon with water lettuce too
• No botanicals are added yet, except for foraged branches and twigs, but there is no visible staining (tank pH = 6.8)
• I'm aiming for a pH between 6.2-6.8, so nothing crazy (the species I plan on keeping aren't super fussy about pH). I'm not looking for advice on how to decrease my pH, since I expect leaf litter to do that well enough on its own
• Running a sponge filter, so no filter compartments or media bags to add anything to
• I have an existing planted 5.5gal which I believe is cycled, but I adopted it, so I didn't go through the cycling process with it. This tank's water is, of course, also very low KH. I seeded the new tank with gravel from this one and was planning on adding filter media from it to the new tank as well to help with seeding. This tank is at a pH of 7.2, so I suppose even if these bacteria are adjusted to low KH, they likely won't survive the pH shift with the humic substances anyway.

Any advice or help is greatly appreciated

 

[dw1305]

Hi all,

I seeded the new tank with gravel from this one and was planning on adding filter media from it to the new tank as well to help with seeding.

You are fine. I'd recommend sand rather than gravel, but that should supply the nitrifiers you need.

I'll put some bits in below, but the scientific paper you need is discussed at UKAPS <"Correspondence with Dr Ryan Newton - School of Freshwater Sciences, University of Wisconsin—Milwaukee">.

The paper that led to the correspondence was "Bartelme RP, Smith MC, Sepulveda-Villet OJ, Newton RJ. (2019). "Component microenvironments and system biogeography structure microorganism distributions in recirculating aquaculture and aquaponic systems". mSphere 4:e00143-19. <"https://doi.org/ 10.1128/mSphere.00143-19">.

Dr Newton says

....... If you do need to add nitrifiers the best source is from an aquaponics or aquaculture system that is already running and removing ammonia. Some water or sediment/soil or part of the biobilter (if there is one) is an excellent starter. Without this source as an inoculum then you could add some roots from plants from any other tank that is running - these are likely to have nitrifiers associated with them. A small clipping put into the tank would be enough.......

Now, I hear that the set of nitrogen-processing organisms in blackwater conditions is completely different than the typical players. Different bacteria, archaea, etc. How do I go about growing them? I imagine I should probably add leaf litter and botanicals now to get to a stable pH before trying any sort of cycling process, correct? Once pH is stable, what steps should I take to make sure the tank can handle fish bioload?

There microbial bit is correct, but you need to ignore the concept of "pH stability", pH is never stable in soft water and it doesn't matter. The way I look at it is that:

• In hard water large changes in water chemistry are required to change pH and
• in soft water small changes in water chemistry cause large changes in pH.

We just need to avoid large changes in water chemistry.

Now, the problem is, of course, that traditional nitrogen cycling requires higher KH and ideally a higher pH.

It doesn't, and that is because traditional cycling doesn't exist. The premise is based on the microbes that you can isolate and grow from sewage treatment works, but they aren't actually the microbes found in aquarium filters. At UKAPS we've also had some discussion with Dr Tim Hovanec <"Dr Timothy Hovanec's comments about Bacterial supplements">.

Many sources I've found recommend simply adding a source of KH to raise it. I really don't want to have to do this, as it would require constant maintenance to keep KH levels up long-term and I'd worry about how bringing the KH back down later would affect the bacterial colony. However, basically all sources say that traditional cycling simply isn't possible with KH below 50ppm.

Just ignore them, there is plenty of scientific literature that has looked at the genes that code for ammonia oxidation, including COMAMMOX Nitrospira that directly convert TAN to nitrate (NO3-).

The tank is planted with frogbit and hopefully soon with water lettuce too

Perfect, have a look at <"What is the “Duckweed Index” all about?">.

cheers Darrel

 

[MacZ]

Softwater works differently.
Definition of softwater: KH below detection with standard hobbyist testkits.
Blackwater is just a type of softwater, as is clearwater and whitewater. With measurable KH your tank doesn't fit the definition for any of them.

Ammonia (NH3) is indeed present in normalized* pH under 7.0 almost exclusively as Ammonium (NH4) because the free H+ ions temporarily complete the molecules to NH4.
You should also be aware: Most pH testkits require a minimum KH of 2° or the results become erratic.
* Testkits have a standard accuracy of +/- 0.5, normalized means, if the + is still 7.0 or below. This also means you can ignore any differences of less than 0.5 points. They don't really matter.

Cycling in the classic sense is not possible in very soft water, because the bacteria that do the nitrogen cycle in "normal" water, are not even present (hence bacteria in a bottle don't work). Other bacteria genera, but mostly archaea, yeasts and fugi take over that roll. Additionally these softwater genera often skip the NO2 (Nitrite) stage and metabolize NH4 directly to NO3.

Botanicals are a good substrate for the aforementioned mikroorganisms. That's why most keepers of softwater tanks use lots of them in their tanks. They also double as free food for most softwater fish.

Concerning pH buffering:
You have basically two systems. One is KH. Straightly described: The higher the KH, the higher the pH. The other system is humic substances (aka "tannins") from botanicals or peat. This system does not work that way, but depending on the amounts of humic acids it settles at a pH between 4.5 and 6.5. It can't go further down without the addition of amounts of humic acids that are toxic anyway.
Only problem is: You have to use the one or the other. You have detectable KH, the humic substances will counter the KH and neutralize it. Once you add water with KH the whole systems starts getting wobbly.
And important: Stable pH is a myth. It will always be dependent on various factors. The ratio of amplitude to period is what makes pH swings dangerous or harmless. High amplitude (e.g. +/- 2 pH points) in a short period (e.g. 10 minutes) is dangerous. High amplitude in a long period (e.g. 2 hours) is safe. That's why people acclimate fish that come delivered in vastly different parameters from their tanks. But also because of osmotic pressure.

For practical advise I'd need some info:
- a picture of the tank
- EC/TDS readings of your tap and the tankwater

Is it possible you've read my blackwater primer on Fishlore? I recognize some of my phrasing in your post. The above info is updated to things I've learned and/or experienced since I've left that site.

And thanks Darrell, you've added the exact links, I would have added.

 

[Seisage]

Softwater works differently.
Definition of softwater: KH below detection with standard hobbyist testkits.
Blackwater is just a type of softwater, as is clearwater and whitewater. With measurable KH your tank doesn't fit the definition for any of them.

Ammonia (NH3) is indeed present in normalized* pH under 7.0 almost exclusively as Ammonium (NH4) because the free H+ ions temporarily complete the molecules to NH4.
You should also be aware: Most pH testkits require a minimum KH of 2° or the results become erratic.
* Testkits have a standard accuracy of +/- 0.5, normalized means, if the + is still 7.0 or below. This also means you can ignore any differences of less than 0.5 points. They don't really matter.

Cycling in the classic sense is not possible in very soft water, because the bacteria that do the nitrogen cycle in "normal" water, are not even present (hence bacteria in a bottle don't work). Other bacteria genera, but mostly archaea, yeasts and fugi take over that roll. Additionally these softwater genera often skip the NO2 (Nitrite) stage and metabolize NH4 directly to NO3.

Botanicals are a good substrate for the aforementioned mikroorganisms. That's why most keepers of softwater tanks use lots of them in their tanks. They also double as free food for most softwater fish.

Concerning pH buffering:
You have basically two systems. One is KH. Straightly described: The higher the KH, the higher the pH. The other system is humic substances (aka "tannins") from botanicals or peat. This system does not work that way, but depending on the amounts of humic acids it settles at a pH between 4.5 and 6.5. It can't go further down without the addition of amounts of humic acids that are toxic anyway.
Only problem is: You have to use the one or the other. You have detectable KH, the humic substances will counter the KH and neutralize it. Once you add water with KH the whole systems starts getting wobbly.
And important: Stable pH is a myth. It will always be dependent on various factors. The ratio of amplitude to period is what makes pH swings dangerous or harmless. High amplitude (e.g. +/- 2 pH points) in a short period (e.g. 10 minutes) is dangerous. High amplitude in a long period (e.g. 2 hours) is safe. That's why people acclimate fish that come delivered in vastly different parameters from their tanks. But also because of osmotic pressure.

For practical advise I'd need some info:
- a picture of the tank
- EC/TDS readings of your tap and the tankwater

Is it possible you've read my blackwater primer on Fishlore? I recognize some of my phrasing in your post. The above info is updated to things I've learned and/or experienced since I've left that site.

And thanks Darrell, you've added the exact links, I would have added.

Thank you Mac. Yes, I have read your blackwater primer haha.

Your notes on pH and its instability are good. Are there any particular things to keep in mind to avoid the rapid shifts? Regarding setup, if my detectable KH is an issue, can I still use leaf litter? It's a hallmark of the biotope I'm going for, but my understanding is that leaves release humic substances, correct?

Unfortunately, I can't give you a number for EC/TDS right now since I don't currently have a way to measure either. I can try asking around, but I'm not sure I'd be able to source a meter for at least a few days. I can give you a tank picture though. Until I can measure TDS, is there anything I can do to help the tank along in the meantime? Essentially, my question boils down to this: how do I set up this tank to be safe for fish? I don't need (or really want) it to be a true blackwater tank, so I suppose my phrasing in my initial post is a bit misleading, apologies. I mostly just want it to be stained and ideally slightly acidic, if possible. My issue is really just the KH, which is too low to support the usual nitrifying bacteria grown in filter media using fishless cycling methods.

 

[MacZ]

Are there any particular things to keep in mind to avoid the rapid shifts?

Don't use hard water for waterchanges and don't use strong acids to achieve ultra low pH. Keep EC/TDS as low as possible (< 50mg/l or 100µS/cm).

Regarding setup, if my detectable KH is an issue, can I still use leaf litter?

Of course you can use it.

Unfortunately, I can't give you a number for EC/TDS right now since I don't currently have a way to measure either. I can try asking around, but I'm not sure I'd be able to source a meter for at least a few days. I can give you a tank picture though. Until I can measure TDS, is there anything I can do to help the tank along in the meantime? Essentially, my question boils down to this: how do I set up this tank to be safe for fish? I don't need (or really want) it to be a true blackwater tank, I mostly just want it to be stained and ideally slightly acidic, if possible. My issue is really just the KH, which is too low to support the usual nitrifying bacteria grown in filter media using fishless cycling methods.

Go the extra step: Use rainwater or RO. Your tap is on the brink and will only make you trouble. Either go full softwater or hardwater, but always on the edge with 1-2°KH is going to make you mad over time.

And you might want to look for another filtration system. Air driven systems drive out CO2 which is part of the balance of KH, pH and CO2. If you drive it out KH and pH will rise effectively.

You won't need a meter immediately. It may take the usual time for delivery, no problem.

The overall setup looks nice, btw.

 

[Seisage]

Don't use hard water for waterchanges and don't use strong acids to achieve ultra low pH. Keep EC/TDS as low as possible (< 50mg/l or 100µS/cm).


Of course you can use it.


Go the extra step: Use rainwater or RO. Your tap is on the brink and will only make you trouble. Either go full softwater or hardwater, but always on the edge with 1-2°KH is going to make you mad over time.

And you might want to look for another filtration system. Air driven systems drive out CO2 which is part of the balance of KH, pH and CO2. If you drive it out KH and pH will rise effectively.

You won't need a meter immediately. It may take the usual time for delivery, no problem.

The overall setup looks nice, btw.

I could use rainwater or RO water currently, but I don’t know for how long. I’m a graduate student/in my early career stages, so I expect to be moving around. Not a lot, but enough that I wouldn’t be comfortable creating a system reliant on a 0 TDS starting point.

Which means I’ll probably just have to abandon the idea of true softwater and aim for a “hard” water of the 3 KH minimum recommended for most fishless cycling methods. In this case, I might actually want to keep my sponge filter, then, if it raises KH, yes? And/or add a bit of crushed coral, probably.

And thank you! I really want this setup to work because I think it could look fantastic once completed and stocked.

 

[MacZ]

I could use rainwater or RO water currently, but I don’t know for how long. I’m a graduate student/in my early career stages, so I expect to be moving around. Not a lot, but enough that I wouldn’t be comfortable creating a system reliant on a 0 TDS starting point.

Zero TDS isn't possible. A small portable RO-System costs about 50€ (convert yourself, please) and fits on an A4 sheet of paper. That's what I use, too. The system reduces TDS down to 5-10mg/l. The result in a tank is at around 30-50mg/l usually.
Thus I see no point in abandoning the project.

I might actually want to keep my sponge filter, then, if it raises KH, yes?

It won't raise it really, just to an effective maximum of what is there already. pH will be higher that way.

A word of warning though: Softwater fish have adapted to it to avoid bacteria. Keeping softwater fish like e.g. cardinal tetras in harder water reliably shows an increase of infections. It's also not the pH but the low conductivity, that keeps the germs away.

 

[Seisage]

Zero TDS isn't possible. A small portable RO-System costs about 50€ (convert yourself, please) and fits on an A4 sheet of paper. That's what I use, too. The system reduces TDS down to 5-10mg/l. The result in a tank is at around 30-50mg/l usually.
Thus I see no point in abandoning the project.


It won't raise it really, just to an effective maximum of what is there already. pH will be higher that way.

A word of warning though: Softwater fish have adapted to it to avoid bacteria. Keeping softwater fish like e.g. cardinal tetras in harder water reliably shows an increase of infections. It's also not the pH but the low conductivity, that keeps the germs away.

Good to know. I live/work at a scientific research station, so we have RO systems, but if it’s better/safer to convert it yourself, then I’ll try the rainwater route until I can save up for an RO unit (edit: my bad! I misunderstood your meaning of “convert” there. I can probably use RO then, but I’ll have to ask to make sure the system is maintained regularly enough). Either way, do you have any particular preferences for remineralization additives?

And, if I’m going the true softwater route after all, that brings my initial cycling question back into play. You mentioned that you can’t give any practical advice without a TDS reading. If we’re now assuming I’m using rainwater or RO and remineralizing to 30-50 mg/L, what would your suggestions be for making this tank safe for fish?

I have read up on the bacteria issue for softwater fish. Just for reference, I plan on stocking neon tetras, hatchetfish, zebra otos, and apistogramma agassizii, all of which do have relatively low tolerance for bacteria. The reasons I chose a sponge filter are twofold. One, I’ve read that they’re better for maintaining low bacteria counts in the water column than other filter types, and they have more surface area to host nitrifying organisms. Two, and probably more importantly, I’d like to have minimal flow in this tank for the biotope and livestock. Would the sponge filter still be too much of an issue in terms of KH/pH?

 

[dw1305]

Hi all,

Which means I’ll probably just have to abandon the idea of true softwater and aim for a “hard” water of the 3 KH minimum recommended for most fishless cycling methods. In this case, I might actually want to keep my sponge filter, then, if it raises KH, yes? And/or add a bit of crushed coral......

You don't have to raise dKH, or do "fishless cycling".

Cheers Darrel

 

[MacZ]

I meant converting from € to whatever currency you are using.

You don't have to raise dKH, or do "fishless cycling".

Exactly the whole point of what you and I said above. Though I'd still recommend letting a tank season a while without fish, just with plants, botanicals and wood.

 

[MacZ]

If we’re now assuming I’m using rainwater or RO and remineralizing to 30-50 mg/L, what would your suggestions be for making this tank safe for fish?

And no. no remineralizing. I add nothing except regular additions of humic substances extrcted from elder cones, leaf litter and rooibos. My tank is at a point I only have to top up to counter evaporation. Just yesterday's readings: 25mg/l TDS / 52µS/cm.

I use a 16 year old 2nd hand canister filter by JBL (with a sponge as a prefilter on the intake) rated for a 250 Liter tank on a roughly 90 Liter net volume, I have several Nymphea lotus thriving, just as the Hydrocotyle and Limnobium, and my biggest pride, a green wall of what I estimate a total 15-20m of vines from 5 Pothos plants (excuse the patches on the wall, we had some roof leakage a few weeks ago). I just weeded the plants out a bit, so it doesn't seem as much.
The water is soft from the start, I stopped adding liquid fertilizers almost 6 months ago and it all grows like weed.
Anyhow: The key is starting with a respectable mass of plants.

 

[Seisage]

I meant converting from € to whatever currency you are using.

Haha, yes, I realized my mistake shortly after posting, oops.

Exactly the whole point of what you and I said above. Though I'd still recommend letting a tank season a while without fish, just with plants, botanicals and wood.

Okay! So, based on our whole discussion thus far, here's what I'm thinking my best next steps for this tank are:
1. Replace current tank water with straight RO or rainwater
2. Add botanicals and/or extracts (is there a good recommended starting level?)
3. Test for pH, GH, KH, etc. to make sure things are where I want them, or maybe just pH if the GH/KH tests are useless at this point
3. Get my hands on a TDS meter
4. Wait!

Does that seem like a roughly reasonable course of action? How long do you usually have to wait to let a tank season sufficiently such that it's safe for fish? I'm guessing probably around 4-5 months, based on what I've read. Would adding invertebrates be beneficial before then? What should I look for in determining whether the tank is ready for fish? And, I imagine I should do slow, gradual additions of fish to give the system a chance to adjust. Is that correct?

Oh, and should I do any water changes during the seasoning process?

And no. no remineralizing. I add nothing except regular additions of humic substances extrcted from elder cones, leaf litter and rooibos. My tank is at a point I only have to top up to counter evaporation.

Anyhow: The key is starting with a respectable mass of plants.

That's actually fantastic news. I know it's not difficult, but I admit I wasn't thrilled at the prospect of having to calculate concentrations and prepare new water every time I add or change it. I'm actually very curious about your lack of water changes. Basically everything I've read about maintaining blackwater systems says that small, frequent water changes are necessary.

Yes, my goal is to start with as many plants as possible. And you should absolutely be proud of your pothos. I'm not sure I've ever seen one that large! Your tank is beautiful too

 

[Ben Rhau]

Once you see vigorous, new plant growth, it's safe to add fish. In such nutrient poor water, this will take some time, as the plants will experience some shock and have to adapt to this environment. I think it can take a couple months.

I don't advise adding inverts until you know the EC/TDS of your water. Inverts don't tend to survive well in blackwater. There are a few, but they do need some mineral content to survive. If you want to keep them, it will be a bit of a compromise.

-B

 

[Seisage]

Once you see vigorous, new plant growth, it's safe to add fish. In such nutrient poor water, this will take some time, as the plants will experience some shock and have to adapt to this environment. I think it can take a couple months.

I don't advise adding inverts until you know the EC/TDS of your water. Inverts don't tend to survive well in blackwater. There are a few, but they do need some mineral content to survive. If you want to keep them, it will be a bit of a compromise.

-B

Would you recommend adding liquid ferts straight away, or wait for the system to establish itself first and use the plants as a barometer without outside help?

Just as well with the inverts, I suppose. I haven't been able to find any Amazon inverts for sale, let alone blackwater ones from the Ucayali.

 

[MacZ]

1. Replace current tank water with straight RO or rainwater

Correct.

2. Add botanicals and/or extracts (is there a good recommended starting level?)

Add leaf litter and combine with extract. As said above botanicals are welcome substrate for essential microfauna. As long as there are no fish you can barely overdose. Once you have fish, new botanicals should be added in smaller portions. Otherwise dangerous oxygen depletion might occur.

3. Test for pH, GH, KH, etc. to make sure things are where I want them, or maybe just pH if the GH/KH tests are useless at this point

Keep in mind pH tests will barely work. If you really have to know pH (i.e. you want to, use a pH meter and add salt to a sample to raise conductivity, then measure in the sample.

4. Get my hands on a TDS meter

Yes.

5. Wait!

Nope:
5. Add easy to grow plants!
Then

6. Wait!

How long do you usually have to wait to let a tank season sufficiently such that it's safe for fish?

4 weeks in my book, though if you have enough plants 2 weeks would work, I guess.

Would adding invertebrates be beneficial before then?

Not except what comes hitchhiking with the plants. I'm happy having worms and similar smaller by-fauna, but it's mostly microscopic stuff and monocellular organisms that are important in this kind of setup.

What should I look for in determining whether the tank is ready for fish? And, I imagine I should do slow, gradual additions of fish to give the system a chance to adjust. Is that correct?

What Ben says on that topic.

Oh, and should I do any water changes during the seasoning process?

Not necessarily. Once the tank is stocked I recommend weekly 30% until you can be sure the tank has broken in.

That's actually fantastic news. I know it's not difficult, but I admit I wasn't thrilled at the prospect of having to calculate concentrations and prepare new water every time I add or change it. I'm actually very curious about your lack of water changes. Basically everything I've read about maintaining blackwater systems says that small, frequent water changes are necessary.

The secret of my tank is simply the mass of plants. That's a biofilter. Also the evaporation (straight AND via the plants) is so big I have no choice but top up with 15-20 Liters a week.

Yes, my goal is to start with as many plants as possible. And you should absolutely be proud of your pothos. I'm not sure I've ever seen one that large! Your tank is beautiful too

It's 5 separate plants. But yeah, thanks.

 

[MacZ]

or wait for the system to establish itself first and use the plants as a barometer without outside help?

Look out for The Duckweed Index! It works wonders.

I haven't been able to find any Amazon inverts for sale, let alone blackwater ones from the Ucayali.

Besides Euryrhynchus shrimp you will barely find anything in the trade, sadly.

 

[Seisage]

@MacZ
Well, I've already got step 5 started with the frogbit! I'll definitely take a look at that Duckweed Index.

And I want to give a massive "thank you" to you, as well as @dw1305 and @Ben Rhau for your knowledge and for your patience with a stressed and confused newbie. You've made this process much less daunting than it was in my head initially. Thank you for taking the time to answer my near-endless questions. It has really helped!

I hope to be able to post positive updates moving forward, ideally with only sporadic questions haha. It'll be a while before I'm able to get my apisto, but I'm glad to have a good path to follow now.

 

[Seisage]

Okay, sorry, I do have one more thing that I'm curious about. Someone on another forum told me that without feeding the bacteria (or nitrifiers in general), the tank can never be "cycled". This makes scientific and logical sense, but would the leaf litter and humic substances be enough of an ammonia source for the nitrifiers to grow? Based on this whole conversation, I imagine the answer from people here is "yes", but I figured I'd ask.

If I were to add ammonia directly, as a sort of insurance and to speed up the process, would that hurt?

 

[MacZ]

Based on this whole conversation, I imagine the answer from people here is "yes", but I figured I'd ask.

Exactly.

 

[MacZ]

If I were to add ammonia directly, as a sort of insurance and to speed up the process, would that hurt?

Leave it. The organisms in your tank will not grow faster with more ammonia, they lack other nutrients. Also too much of it raises pH as ammonia is a base. It counters H+, resulting in ammonium. And this in turn is mostly used by plants.