Help with changing water chemistry

[threecharacters]

I've been having some trouble matching the water chemistry of Lake Tanganyika. For reference my tap water is 7.8 pH with gH = 4 deg.

I've successfully been raising the gH to 11-12ish. The tank has play sand, a bit of crushed coral, and 12ish snail shells. I've also been adding Equilibrium to the water. The pH is raised slightly compared to tap (8.0). Equilibrium won't change the pH by design (its sulfate based?). Should I get a water additive that specifically raises the KH (and thus pH) or should I wait to see if the coral I added boosts the pH?

This website is interesting. If I'm understanding it correctly, most of the carbonate in Lake Tanganyika is from magnesium, not calcium. In fact, Malawi and Tanganyika have similar calcium contents (actually Malawi has more calcium), but Malawi has a lower pH and gH. It looks like much of the alkalinity of Tanganyika comes from magnesium carbonate? Also Tanganyika has much more potassium, sodium, and chloride than Malawi.

Equilibrium is specifically sulfate based, which means I don't think it will change pH. Thus, I think I need to find something that will dose carbonates! I think want more magnesium carbonates than calcium? Should I also dose with some salts to raise the potassium, sodium, and chloride content of the water? Does anyone have any suggestions for products that will do this?

 

[Byron]

Equilibrium is not going to do anything for the fish. I went into this with Seachem a few years ago. The GH may rise but they said one should not rely on this for fish needs, only plants.

You have two options. My preference is to use a calcareous substrate (play sand is inert, I have it in all my tanks but they are all soft water species). There are substrates specifically made for rift lake conditions and this is one good method as it is basically permanent. There is an aragonite sand that I have used many years back. Water changes have to be carefully handled however, as a massive influx of very soft water could be problematic for the fish.

The second method is to prepare the water with the rift lake salts. Thee are not "salt" as in sodium chloride, but mineral salts designed to replicate the rift lakes water.

You do not have to fuss over specific pH provided it is high (basic, high 7's and up). Adding substances like coral will raise pH but not the GH, or marginally; I've gone down this road too.

 

[Colin_T]

Dead coral skeleton or rubble will raise the pH to 8.5, as will limestone and shells.

I'm pretty sure Lake Tanganyika has more calcium than magnesium.
The chart on the link you provided is a bit hard to follow. It has the following:

"Total hardness as calcium carbonate".
"Total calcium as calcium carbonate".
"Total magnesium as calcium carbonate".

I'm not sure this is correct because magnesium and calcium are different minerals.

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The following link is what I used for my Rift Lake tanks and also to increase the GH for my rainbowfish.
https://www.aquasonic.com.au/NH232/Riftlake-Water-Cond.-250gm/pd.php

Aquasonic Rift Lake conditioner, list of ingredients: sodium chloride, sodium carbonate, magnesium chloride, magnesium sulphate, calcium chloride, calcium sulphate, potassium chloride, potassium nitrate, lithium chloride, sodium bicarbonate, sodium thiosulphate.
Directions for use: add one level teaspoon per 7 liters of water.

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The directions for use is not really that accurate. You need to work out the GH of your water before you add some and test it again 24 hours after adding it. If you have hard water to begin with you don't need to add as much. If you have really soft water you might need to add more.

Rift Lake salts need to be added to a container of water and aerated for 24 hours before using the water in a tank containing fish.

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Sodium thiosulphate is use to neutralise chlorine in water. It's the main ingredient in dechlorinators.
Anything with chloride at the end will increase the GH.
Anything with carbonate or bicarbonate will raise the KH and pH.

No idea what potassium nitrate is meant to do for fish. I'm pretty sure it is used to make bombs and gun powder. All I can think of now is the shell dwellers throwing bombs at each other.

 

[seangee]

Just to add balance my preference would be to use an inert substrate and add rift lake salts. That way you have absolute control over what goes in and don't have to worry about large water changes.

I won't use Seachem's stuff because

1. They want you to buy lots of products
2. You have to do complex calculations

I have 2 tubs of equilibrium I bought for a particular tank. When I realised I also needed pH up and pH down and then had to work out the ratios I just bought some mineral salts as suggested. I simply put the same quantity into every bucket I add and the water is always where I want it. Oh and the equilibrium made my water cloudy - the claims that it will dissolve completely did not work for me (at least not within 48 hours).

Also agree about pH - get your GH and KH right and your pH will automatically be in a suitable range, the actual value does not matter.

 

[threecharacters]

OK, I think I'm starting to understand everything.

I used to think KH was a subset of GH, i.e. GH measured KH plus other non-carbonate sources of water hardness. This is wrong. GH is specifically metals (K, Mg, Na, Ca, etc.) which are required by plants to grow properly. KH is specifically carbonate (CO3). This means adding calcium does nothing to raise the pH unless it's in carbonate form. Carbonate can apparently raise the pH of water, presumably by removing hydrogen ions from solution? Metals don't do that. If you add calcium carbonate you raise both GH and KH because you are adding metal cations (calcium) and carbonate anions (carbonate). However, because of the relative weights of the metals to carbonate you probably add more mg/l of carbonate than calcium when adding pure calcium carbonate, thus you raise the KH more than the GH.

Finally, it probably doesn't actually matter how much calcium or magnesium you have exactly. It's more important to get KH, GH, and pH as close to Tanganyikan as possible. How much of the GH is from Ca vs Mg is likely not important.

I have a feeling that my local water supply has a higher KH than GH. KH acts as a pH buffer, i.e. it maintains the pH of the water. I have a 29 gal blackwater aquarium with loads of decomposing leaf litter and wood. The pH of that tank is 7.8, the same as the tap. The water looks like tea but the pH is still the same as the tap because the carbonate in the tap is maintaining the pH. We'll see when I measure it though!

In the end, I'll just get a Tanganyikan specific buffer and use it instead of Equilibrium, which is really just for plants because it lacks carbonate.

 

[seangee]

That's about the sum of it. The salt I use increases GH:KH in the ratio 2:1. So for my shrimp tank I add one teaspoon per 10 litres of RO water to reach dGH 6 and dKH 3. If I were to add 2 spoons I would get 12:6 - and so on. The shrimp tank has a pH of 7, the softwater RO tank has a pH of 6.5, but I don't do anything to change it in either tank.

I don't use tap water because apart from being very hard it contains 50ppm of nitrates. The only downside of increasing the KH more in your water is that you will get more limescale, but it won't affect your GH significantly, and your water will always be alkaline (which is what you want).

 

[Essjay]

GH is more specific than that. It measures only divalent metal ions; of these metal ions, calcium is the one present in greatest quantity with magnesium next. There are small amounts of other metals. Sodium and potassium are monovalent so are not included in GH, neither are trivalent metals like aluminium.
GH is expressed as though all the metals were calcium carbonate (you'll see the phrase 'as mg/l calcium carbonate') or even calcium or calcium oxide. Hardness "as mg/l calcium" is common with UK water companies.

KH is the amount of buffer in the water. The most common chemical is carbonate and bicarbonate. KH doesn't measure carbonate as such, it is measured by adding acid of a specific concentration until the pH drops to 4.5. This is why water companies use the term alkalinity rather than KH.


My son is a PhD chemist who used to work for a water testing company

 

[threecharacters]

That's about the sum of it. The salt I use increases GH:KH in the ratio 2:1. So for my shrimp tank I add one teaspoon per 10 litres of RO water to reach dGH 6 and dKH 3. If I were to add 2 spoons I would get 12:6 - and so on. The shrimp tank has a pH of 7, the softwater RO tank has a pH of 6.5, but I don't do anything to change it in either tank.

I don't use tap water because apart from being very hard it contains 50ppm of nitrates. The only downside of increasing the KH more in your water is that you will get more limescale, but it won't affect your GH significantly, and your water will always be alkaline (which is what you want).

50ppm nitrates in tap water sounds like it should violate some water quality regulations! My water supply is 0 ppm for ammonia, nitrite, and nitrate

GH is more specific than that. It measures only divalent metal ions; of these metal ions, calcium is the one present in greatest quantity with magnesium next. There are small amounts of other metals. Sodium and potassium are monovalent so are not included in GH, neither are trivalent metals like aluminium.
GH is expressed as though all the metals were calcium carbonate (you'll see the phrase 'as mg/l calcium carbonate') or even calcium or calcium oxide. Hardness "as mg/l calcium" is common with UK water companies.

KH is the amount of buffer in the water. The most common chemical is carbonate and bicarbonate. KH doesn't measure carbonate as such, it is measured by adding acid of a known strength until the pH drops to 4.5. This is why water companies use the term alkalinity rather than KH.


My son is a PhD chemist who used to work for a water testing company

Thanks for this info! I probably would've never found it otherwise. Also the "as mg/l calcium carbonate" units in the link I posted above make sense now.

 

[seangee]

50ppm nitrates in tap water sounds like it should violate some water quality regulations! My water supply is 0 ppm for ammonia, nitrite, and nitrate

It certainly should. The EU limit is 50ppm so they do just enough to stay out of trouble. According to the WHO the limit is perfectly safe to drink but suggest you don't if you happen to be pregnant or under 2 years old - so obviously not that safe.

 

[Byron]

It certainly should. The EU limit is 50ppm so they do just enough to stay out of trouble. According to the WHO the limit is perfectly safe to drink but suggest you don't if you happen to be pregnant or under 2 years old - so obviously not that safe.

There is also a difference in "nitrate" between our aquarium tests and professional water authorities. I had another member explain this to me a few years back, but sadly I have forgotten most of it and won't guess. But the point is that 40ppm with our tests like the API is so far as I can remember much different from the water authority's guide.

This excerpt from an online article of Cornell University (USA) may illustrate. The full article is at:
http://psep.cce.cornell.edu/facts-slides-self/facts/nit-heef-grw85.aspx

Nitrate in drinking water is measured either in terms of the amount of nitrogen present or in terms of both nitrogen and oxygen. The federal standard for nitrate in drinking water is 10 milligrams per liter (10 mg/l) nitrate-N, or 45 mg/l nitrate-NO3. when the oxygen is measured as well as the nitrogen. Unless otherwise specified, nitrate levels usually refer only to the amount of nitrogen present, and the usual standard, therefore, is 10 mg/l.
​

Again, this is in the US; UK may be different, essjay might know.

 

[seangee]

There is also a difference in "nitrate" between our aquarium tests and professional water authorities. I had another member explain this to me a few years back, but sadly I have forgotten most of it and won't guess. But the point is that 40ppm with our tests like the API is so far as I can remember much different from the water authority's guide.

That may be the case - but the API test measures my tap water as 40ppm and other aquarium tests, using a different scale, show it as 50.

 

[Byron]

That may be the case - but the API test measures my tap water as 40ppm and other aquarium tests, using a different scale, show it as 50.

That seems incorrect. The API test uses the nitrate-NO3 scale, and the other scale (nitrate-N) would read a lower number for the same water sample. So if the API tests at 40ppm, the nitrate-N number would be a lower number. ??

Safe nitrate for the hobby assumes we are all using the basic tests like the API, so no one should conclude 40 ppm is safe because the nitrate-N test would be 10 ppm or whatever.

 

[Essjay]

The two ways of measuring nitrate are as nitrate-NO3 and nitrate-N. The difference is that nitrate-NO3 measure nitrate as the whole nitrate; nitrate-N measures just the nitrogen part of nitrate.

Nitrate-NO3 is what our test kits and UK water companies use. My water quality report gives the upper limit for nitrate as "50 mg/l as nitrate", ie nitrate-NO3.
American water companies use nitrate-N.


50 mg/l nitrate-NO3 converts to 11.3 mg/l nitrate-N, so EU and American maximum limits in drinking water are virtually the same.

 

[seangee]

Nitrate-NO3 is what our test kits and UK water companies use. My water quality report gives the upper limit for nitrate as "50 mg/l as nitrate", ie nitrate-NO3.
American water companies use nitrate-N.

Yup just checked on the DWI site (drinking water inspectorate). Its definitely stated as mg/l of NO3.