peat granules to lower PH and soften water?

[Neil Groves]

I have city water of 7.6pH and I have just bought a HOB filter so I can use peat granules to lower this hopefully to around 6.5pH, my question is what quantity do I use? has anyone else used peat granules and can advise me please?

Neil.

 

[gerald]

Depends on your KH and GH. If they are low like my tapwater (~2 degrees or 35 mg/L), pH will drop anyway without adding peat, because ammonia-processing by bacteria will release acidic H+ ions. This process may start slow, but pH can drop fast after the KH is used up.

 

[Neil Groves]

I put my peat granules in my HOB filter yesterday and so far no colour change in my water which is good, how long before I can expect to see my pH start to fall? I need to drop from 7.8 pH to 6.8 pH if possible.

Neil.

 

[dw1305]

Hi all,

I put my peat granules in my HOB filter yesterday and so far no colour change in my water which is good, how long before I can expect to see my pH start to fall? I need to drop from 7.8 pH to 6.8 pH if possible.

If the water doesn't tint the pH won't change. It is the humic and tannic substances that both tint the water and lower pH.

Depends on your KH and GH.

Is the answer to when, and whether. If your water has a lot of bases (high dGH/dKH) the peat won't lower the pH because all of its ion exchange sites will be filled, and the peat exhausted, before the pH changes.

Have a look at <"Another Peat filtration ...">.

cheers Darrel

 

[boofeng]

I recently started using peat moss from gardening centres, after checking out various threads including those here - thanks very much to those who've blazed the way.

Tapwater (with Prime) = pH 7+, dGH 5, dKH 3
After peat filtration = pH 4+, dGH 3, dKH 0

I guess KH goes to zero because the bicarbonate equilibrium is shifted by the fulvic/humic/tannic acids. But why doesn't GH go to zero, and instead only gets reduced to a certain value? I notice other users previously have similar results as myself.

 

[gerald]

Adding acids destroys KH (bicarbonate and carbonate) by converting it to CO2, so it's actually gone from the water. GH (Ca+ and Mg+ ions) can't be destroyed or removed as easily. They can only be absorbed (adsorbed?) onto some material (resin, leaves, wood, peat) by ion exchange, or into the cells and shells of animals or plants. Once the peat is fully saturated with Ca and Mg, it can't adsorb any more, as Darrel said above. Using new peat might remove more of the GH.

 

[regani]

Gerald is correct, only Ca and Mg ions that get adsorbed to the surface of the peat or resin get actually removed from the water column.
There is an additional issue with GH measurements in water containing tannins, humic/fulvic acids etc. for example as in water treated with peat. Those natural acids not only destroy KH and lower pH, they are also good complexing agents, meaning they are able to 'mask' Ca and Mg ions by wrapping themselves around them. This can reduce bioavailability and also their contribution to conductivity - it is difficult to find good data here as tannins, humic acids etc. are poorly defined mixtures that can vary quite a bit depending on where they come from.
The reagents used to measure GH are designed to free all calcium ions from complexes such as formed by e.g. humic acids.They are much stronger complexing agents and have to be, so that the kit can give you a reading on the true concentration of Ca and Mg ions including the ones that are hidden away in weaker complexes.
So even though you get a GH reading it may not tell you that much about the true effect of the Ca and Mg on the fish. The more useful measurement in this case is conductivity.
I hope the above makes at least some sense?

 

[boofeng]

Thanks gerald and regani. You all have definitely helped me understand things better. And make me feel more assured about the effectiveness of peat filtration.

Right now, my guesses are:

1. Some Ca and Mg is stuck on the peat - this makes up the loss in measured gH.

2. Some Ca and Mg are still in the water, but bound to chelating agents like tannic, humic, other acids - this is still picked up by the gH test kit.

3. The actual effects of Ca and Mg to fish and (especially!) their eggs are probably different from what I see on the gH test reading. Because their bioavailability in the presence of organic acids are not easy to study and document. Hopefully it is less!

I realise I forgot to provide TDS values earlier: before peat treatment mine is 110-120, and after peat treatment it is 95-105. Again, I guess organic acids mess with TDS values too - so I'm not worried that it's not going down as much as gH. Ideally I'll target a low TDS value (using DI water) because that's nearer to most apistos' natural habitats - but in practice the DI unit is slow and resin expensive, so I'll stick to peat and keep DI water in reserve for special situations.

 

[regani]

It gets a bit complicated with those organic acids and conductivity and TDS. When you add some of those organic acids to water the KH and pH will drop and measured GH won't change (although bioavailability may). The conductivity will drop because they mask the Ca and Mg ions and the actual TDS will go up. I did that experiment with citric acid once, which is a good substitute for fulvic and tannic acids, and got those results (didn't measure TDS, though).
The measurement you see on a TDS meter is in fact a conductivity reading multiplied with a factor that is often based on fertiliser concentrations in hydroponics to give you a number that is close to actual TDS. But in case of those organic acids the real TDS (total dissolved solids) will go up, because you are adding additional things to the water. The proper way of measuring TDS would be to evaporate all the water in a sample and then accurately weigh the residue.
But a TDS meter will still serve you well as you can see if your conductivity goes up or down even if the values it shows on the display are not an accurate reading of anything, really
Your water will likely be ok for a range of species and you can try to lower conductivity by doing a second peat filtration (removing more GH) or by diluting with RO water where necessary.

 

[boofeng]

It gets a bit complicated with those organic acids and conductivity and TDS. When you add some of those organic acids to water the KH and pH will drop and measured GH won't change (although bioavailability may). The conductivity will drop because they mask the Ca and Mg ions and the actual TDS will go up. I did that experiment with citric acid once, which is a good substitute for fulvic and tannic acids, and got those results (didn't measure TDS, though).
The measurement you see on a TDS meter is in fact a conductivity reading multiplied with a factor that is often based on fertiliser concentrations in hydroponics to give you a number that is close to actual TDS. But in case of those organic acids the real TDS (total dissolved solids) will go up, because you are adding additional things to the water. The proper way of measuring TDS would be to evaporate all the water in a sample and then accurately weigh the residue.
But a TDS meter will still serve you well as you can see if your conductivity goes up or down even if the values it shows on the display are not an accurate reading of anything, really
Your water will likely be ok for a range of species and you can try to lower conductivity by doing a second peat filtration (removing more GH) or by diluting with RO water where necessary.

I've let the water sit in the "peat filter" (a beverage dispenser actually) for 24++ hours before, and the measured TDS (or conductivity rather) doesn't go down appreciably more - at best the meter reads 90+, from a potential max of 130+ out the tap. So I think there is a lower bound on how much peat can reduce conductivity (whatever effect that actually has for the fish! ).

Sorry I'm not sure what result you obtained with citric acid - do you mean you managed to reduce KH and pH, but measured GH didn't change?

I've actually read that 700 litre Amazon thread Darrel referenced where you talked about citric acid (very grateful for that ) - that's what made me try citric acid myself. My experience with it is that the pH bounces back up after a couple of days? I actually brought the candidi tank down to pH 4.0 with citric, but it rose back to high 6+ again. TDS didn't go up appreciably though, it started at 140ish and was 150ish after adding citric acid. (Didn't test GH and KH then.) Maybe the substrate was buffering it back up (it's a mix of sand and ADA Malaya)? Or the citric acid is decomposing fast somehow? IIRC I saw some document stating citric acid has a half-life of two days in water, though I'm sure this is highly variable depending on environment.

Anyway, thanks for all the tech talk - appreciate all the geekiness. (Darrel, I've been stalking your old posts about which plants to try in soft water too - and I'm absolutely on board with your BOD concept - I'm incorporating wet/dry trickle filters as much as possible in my future tanks.)

And in real world terms, I'm all sorted with peat filtration and RO, like you've said, Regani, so I'm one happy camper. Cheers!

 

[regani]

The addition of citric acid gave a reduction in pH, KH and conductivity, no change in measured GH.

Yes, citric acid degrades over time, that is why I use a mix of hydrochloric and citric acid. The job of the hydrochloric acid is to bring down the pH, the citric acid brings down conductivity by complexing Ca and Mg. These complexes are also less susceptible to degradation, I believe - I haven't found specific data but it is the case most complexes with labile ligands.
Weekly water changes gave me stable water values, though, if that counts as an experimental proof.
The degradability of citric acid is one of the reasons while I chose it over EDTA and the like - those stay around much longer and can accumulate in your tank, potentially leading to problems down the road.

 

[dw1305]

Hi all,

....I'm absolutely on board with your BOD concept - I'm incorporating wet/dry trickle filters as much as possible in my future tanks.)

I think because I came back to fish-keeping from a different (waste water treatment) perspective, it gave me a fresh insight that I don't think I would have had if I'd always kept fish.

cheers Darrel