Pure R/O or Distilled water health effects

[TCMontium]

Hi,

I usually see measurements of 1-50 microSiemens of conductivity from wild collection sites of many dwarf cichlids, tetras and pencilfish etc. And some internet articles such as Seriouslyfish pages recommend water with close to or straight up 0 ppm TDS for many low pH preferring species. But I almost always see people use a mix of tap and R/O or rain or distilled water for their aquariums of such species. Is only using distilled or R/O water unhealthy for the fish even though they do live in extremely low conductivity and soft water in the wild? I personally used R/O water without mixing it with any mineral additions or tap water to breed and grow some species but I don't know if that was somehow harmful even though I noticed no problem with the offspring. The aquarium water from the use of only R/O was around 10 microSiemens constantly.
Maybe long time negative health effects that I don't know about are caused from lack of minerals or electrolytes?

 

[MacZ]

For species that are usually adapted to those parameters it is fine to use straight up RO.

Only things to keep in mind: Are they wild caught or tankbred? Did they live in higher TDS water at the store/trader/breeder for at least a while?
Many breeders will grow out F2 or F3 generations in tap water on purpose, so they can be sold to a wider array of buyers and not just nuts like us here, that use straight up RO. Interestingly it's always possible to keep decidedly soft water species in harder water (to a degree at least), because their gills and kidneys are adapted to retaining more minerals and electrolytes. Going the opposite, hardwater species are adapted to get those out of their bodies in larger amounts, so in too soft water they go down due to the osmotic pressure.
So e.g. you can keep cardinal tetras in 15°GH and 10°KH water with a pH of 8 (they won't do great, but they'll live 2-3 years), but a Tanganyikan cichlid in 2°GH and 0°KH with a pH of 6.5 will be dead within 2-3 weeks.
For many farmbred fish this whole thing has become irrelevant, though. Domestic strains of Apisto can be kept in almost any conditions and will do quite well.

So anyhow, if the fish have lived in tap for a while it's necessary for many species to raise the percentage of RO slowly, so they gill-filaments can adapt (again). Usually takes a week with several waterchanges.

Some people want to absolutely make sure their fish get enough minerals and so they keep the GH at a minimum level of around 3-5°. From a physiological standpoint that's not supported, but also not bad for the fish. They should be able to take their minderals just from their food and chewing the substrate.

Others keep the KH up, to prevent pH-crashes. Also not rooted in science, as for a pH-crash certain conditions must be in place, and just having a KH of 0 alone is not that. What many people seem not to get is, that a pH-crash is seen from a standpoint of trying to keep the water at a neutral pH, not an acidic pH. Peat, leaf litter beds and botanical extracts buffer pH very well, just not in neutral territory.

What keeps many "casual keepers" (read: people that dn't want to breed their fish) from going 100% RO are actually the plants. When you reduce the water to basically pure water, there are no nutrients for the plants. And thinking how low the stocking density in most blackwater tanks is and how little nutrients are in dead, brown leaves and driftwood, it's no wonder many plants will just melt away in pure RO water.

I use about 90% RO, 10% tap with the lowest possible amount of fertilizers (macro and micro), so my plants don't melt away. Without fertilizers and the same water mix I lost 50% of plant mass within 2 weeks, even floating plants like frogbit and salvinia basically dying out. TDS are between 50-70mg/l, EC maxes out at 130µSI, pH is just below 6, NO3 has to be added, otherwise it's down to less than 10mg/l between waterchanges and at that point some plants develope deficiencies.
But my fish are extremely content. The Pencilfish are spawing all day, cardinal tetras have the greatest colours and the Apistogramma is in top shape as well.

 

[TCMontium]

Thanks for all the information, very helpful answer.
All my fish except cardinal tetras were listed as wild caught fish, so I suppose I should keep them without mixing and tap water or maybe just a little.
I do plan to slowly acclimate the juveniles of the fish I breed to 100% tap water as well, just because people will most likely keep them in tap water without mixing any R/O or distilled water to it.

On a little side note I guess some plant species like Hydrocotyle leucocephala, Limnobium laevigatum and Salvinia sp. can grow pretty well even in extremely soft water without any fertilizers. The one aquarium that I never dare put any tap water into had these plants flourishing for several years. The conductivity in the tank changes between 5 to 50 microSiemens depending on if I used distilled or R/O for water changes and how often I changed the water etc. The tank is purely a breeding aquarium so I always only had a pair of dwarf cichlids or just no fish in it (and the eggs never hatched until this month, so there was no nutrients for the plants from heavyly feeding the fry either). The Hydrocotyle does mostly grow outside the water by climbing on the glass and cables so pretty much all the leaves of the plants are outside the water, only the roots are in the water (2 of the plant species are surface plants afterall). Maybe growing outside the water, closer to the light has something to do with them doing so well, combined with the fact that the closed lid is making the air very warm and humid inside.

 

[MacZ]

All my fish except cardinal tetras were listed as wild caught fish, so I suppose I should keep them without mixing and tap water or maybe just a little.

Cardinals are usually not listed as WC in Germany, but still are mostly. Only about 20% of the specimens offered here are tankbred from the Czech Republik or Israel. Mine were not listed as WC, but do great in my water and seem wc specimens nonetheless.

On a little side note I guess some plant species like Hydrocotyle leucocephala, Limnobium laevigatum and Salvinia sp. can grow pretty well even in extremely soft water without any fertilizers.

I have exactly that combination in my tank, Limnobium and Salvinia went extinct twice before I started using fertilizers (and I'm really glad I already had a small nano tank just for plants where I keep spare plants so I don't have to buy or trade in such cases), Hydrocotyle melted down and only grew micro-leaves at the same time. The water hardness was no problem, still isn't, but the lack of any nutrients was their doom. Even with being grown only at the surface and partially fully emersed. For sure getting atmospheric CO2 and a moist warm environment help, but nutrients are still necessary.

I would assume the nutrients from the lighter feeding and probably when parts of the plants died back balanced out exactly. Have you measured NO3 as an indicator for nutrients at any point?

The conductivity in the tank changes between 5 to 50 microSiemens depending on if I used distilled or R/O for water changes and how often I changed the water etc

When have you last changed the membrane of your RO-unit? If the RO has more than 10-15 µSI I'd change it asap.

Edit: Here a picture of the state of my plants few minutes ago. Please note, that I also have a big Pothos plant which sucks nutrients like nothing else.

 

[TCMontium]

Cardinals are usually not listed as WC in Germany, but still are mostly. Only about 20% of the specimens offered here are tankbred from the Czech Republik or Israel. Mine were not listed as WC, but do great in my water and seem wc specimens nonetheless.

Interesting, I thought neons and cardinals were both mostly captive bred at this point. Good to know.

I have exactly that combination in my tank, Limnobium and Salvinia went extinct twice before I started using fertilizers (and I'm really glad I already had a small nano tank just for plants where I keep spare plants so I don't have to buy or trade in such cases), Hydrocotyle melted down and only grew micro-leaves at the same time. The water hardness was no problem, still isn't, but the lack of any nutrients was their doom. Even with being grown only at the surface and partially fully emersed. For sure getting atmospheric CO2 and a moist warm environment help, but nutrients are still necessary.

I would assume the nutrients from the lighter feeding and probably when parts of the plants died back balanced out exactly. Have you measured NO3 as an indicator for nutrients at any point?

when I take some Hydrocotyle out of the tank and put it in other aquariums with soft water they also melt to a point and then develope micro leaves and more pale colors. These other aquariums have no lid and different lighting types so I assume that has the most effect. Water is also a little bit more conductive and much more heavyly populated with fish but those are supposed to be better for the plants afaik rather than cause them to melt and develope micro leaves. But about 2 years ago when some Hydrocotyle climbed out of the water in one of these aquariums it flourished with big bright leaves.
I measure NO2 and NO3 levels every now and then with strip tests, they are always 0 or almost 0 in the breeding tank with all the healthy plants. Others where plants seem to do worse are also usually around 0 but sometimes before water change they can have around 25 mg/L of NO3.

When have you last changed the membrane of your RO-unit? If the RO has more than 10-15 µSI I'd change it asap.

I have no R/O unit at home for some complicated reasons. I buy R/O water from my pet store. Their R/O water measures around 20 microSiemens when I measure it but I'm not sure if my measuring device is that precise. Even when I use distilled water the water in the breeding aquarium becomes more conductive with the addition of peat, dried leaves, cones, feeding the fish etc. I am pretty sure all the sand and equipment did never bubble to an acid test so they shouldn't be dissolving into the water. There were times where the conductivity in the breeding tank stayed around 6-10 microSiemens for many months anyways so everything in it should be safe.

 

[MacZ]

Interesting, I thought neons and cardinals were both mostly captive bred at this point. Good to know.

Common neon tetras are almost all tankbred. It's just the cardinals that are mostly wild caught.

when I take some Hydrocotyle out of the tank and put it in other aquariums with soft water they also melt to a point and then develope micro leaves and more pale colors. These other aquariums have no lid and different lighting types so I assume that has the most effect. Water is also a little bit more conductive and much more heavyly populated with fish but those are supposed to be better for the plants afaik rather than cause them to melt and develope micro leaves. But about 2 years ago when some Hydrocotyle climbed out of the water in one of these aquariums it flourished with big bright leaves.
I measure NO2 and NO3 levels every now and then with strip tests, they are always 0 or almost 0 in the breeding tank with all the healthy plants. Others where plants seem to do worse are also usually around 0 but sometimes before water change they can have around 25 mg/L of NO3.

There are only a limited number of deficiencies that cause melting and micro leaves, Nitrogen or Calcium usually. switching the tanks may also cause this by itself, as many plants have to adapt.
So if you have readings of 25mg/l of NO3 it might be low calcium. I'm really starting to presume the low conductivity tank has reached that "holy grail"-equilibrium and it might be the plants use straight up ammonium instead of NO2 or NO3.

I have no R/O unit at home for some complicated reasons. I buy R/O water from my pet store. Their R/O water measures around 20 microSiemens when I measure it but I'm not sure if my measuring device is that precise. Even when I use distilled water the water in the breeding aquarium becomes more conductive with the addition of peat, dried leaves, cones, feeding the fish etc. I am pretty sure all the sand and equipment did never bubble to an acid test so they shouldn't be dissolving into the water. There were times where the conductivity in the breeding tank stayed around 6-10 microSiemens for many months anyways so everything in it should be safe.

20µSI are still ok, at 50 I'd be wary.
I just realised I used the wrong unit: I meant ppm or mg/l for TDS. If those reach 10-15 it's too high.
Buying that stuff must be quite expensive over time. Before I got my own RO unit I paid almost 50€ a month (10 a week) for distilled water and had to drag that stuff home on foot with a shopping cart.

 

[TCMontium]

Yeah buying R/O water is certainly more expensive than buying a R/O unit. I pay 20 cents per liter and carry 25-30 liters to my home from the pet store everytime with shopping bags and a backpack. Thankfully both the store and my home are very close to tram stations. Distilled water at grocery stores costs me 30-40 cents per liter. Sadly I just have to buy and carry the water because of the conditions at the current place I'm living in. I'll move out in a few months, then I can hopefully use a R/O unit at home again.

 

[MacZ]

Closest (10min on foot) for me is a hardware store (Hellweg), 5l distilled for 1,49€, I needed 30l-50l a week. So quite expensive. At least now I can use the canisters for the RO.
Next fishstore is 45min by tram, bus and foot (need all of them to get there), and they don't sell RO. So that never was an option.

 

[dw1305]

Hi all,

Maybe long time negative health effects that I don't know about are caused from lack of minerals or electrolytes?

Probably not, if the fish are getting a good diet.

Black-water organisms are fantastically good at accumulating scarce resources, which is one of the reasons they struggle in less nutrient depleted conditions, where "luxury consumption" can occur.

<"Tannic and humic substances"> may play an important role in regulating <"ion uptake in black-water fish">.

cheers Darrel

 

[anewbie]

I have at least 10 confirmed wild caught cardinals and at least 8 tank bred cardinals. I keep them in water that is gh 7 kh 3 and tds 120. They have done fine - my eldest is 3 years old. My understanding is that cardinals are much more difficult to breed than neon but there is a place in florida that does some breeding (I'm told don't know factually). My understanding is wild neon are much heartier than tank bred neon due to over inbreeding.
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One tidbit on cardinals - esp the wild ones - when i first put them in the tank they went into semi-shock but once they saw the other cardinals it took only a few minutes for them to retain full colour and join the flock. It seems that they really feel much better in a larger group (I have around 23 in a 120):

 

[MacZ]

My understanding is that cardinals are much more difficult to breed than neon

Which is correct. They need extremely low conductivity and pH to even really get ready to spawn, additionally the eggs and larvae are highly photosensitive. Producing them in commercial numbers is less sustainable and environment friendly than collection in the wild. (Which has the side effect of offering locals in the amazon basin jobs in sustainable fishery instead of destructive trades like mining or timber industry.)
And yes, wild caught neons (haven't seen confirmed specimens of those in the flesh in years, last time maybe 1996) are not only hardier than tankbred, they are also easily 1-2cm bigger.