Kalkwasser increasing calcium too much while maintaining alk stable

[anthony1222]

Hey, I have an 84 gallon tank and I'm dosing 749 mL of saturated kalkwasser to maintain 0.29 dkh consumption. My calcium keeps going too high at around 520-550 even though my alkalinity stays the same. I have 3 coral frags one an LPS and 2 SPS with coralline algae growing all over the rocks. My magnesium levels are about 1260-1280 and my alk stays at around 8.3. I'm measuring with an apex trident. How do I fix this imbalance?

 

[skey44]

Water changes should help to balance this. Also hobby level calcium testing is pretty unreliable. I would do your water changes and not worry with it very much.

 

[EnterName]

Usually 0.29dKH would balance with a calcium consumption of approx. 2.07ppm Ca, but calcium and alkalinity consumption do not always balance, which might be the reason for the measured parameters. However, @skey44 is absolutely right that calcium test kits aren't too reliable and water changes would ensure the ion balance remains stable without you having to rely on test kits.

If you can't be bothered with water changes, and you are absolutely sure calcium is too high, you could pause adding Kalkwasser and use an alkalinity solution based on for example sodium bicarbonate. This would keep alkalinity stable while calcium gets consumed.

You need to add a total of 92.21dKH daily to match your 0.29dKH consumption rate, which would be equal to 66mL of a 0.5mol NaHCO₃ (1400dKH/L) solution. You can create such a solution by dissolving 42g NaHCO₃ in 700mL of water and filling up to 1L after fully dissolving it.
You can also use Tropic Marin's Original Balling Part B of which you would only need 33mL as it contains 2800dKH/L.

 

[anthony1222]

Usually 0.29dKH would balance with a calcium consumption of approx. 2.07ppm Ca, but calcium and alkalinity consumption do not always balance, which might be the reason for the measured parameters. However, @skey44 is absolutely right that calcium test kits aren't too reliable and water changes would ensure the ion balance remains stable without you having to rely on test kits.

If you can't be bothered with water changes, and you are absolutely sure calcium is too high, you could pause adding Kalkwasser and use an alkalinity solution based on for example sodium bicarbonate. This would keep alkalinity stable while calcium gets consumed.

You need to add a total of 92.21dKH daily to match your 0.29dKH consumption rate, which would be equal to 66mL of a 0.5mol NaHCO₃ (1400dKH/L) solution. You can create such a solution by dissolving 42g NaHCO₃ in 700mL of water and filling up to 1L after fully dissolving it.
You can also use Tropic Marin's Original Balling Part B of which you would only need 33mL as it contains 2800dKH/L.

I do weekly 10% water changes with red sea blue bucket

 

[EnterName]

I do weekly 10% water changes with red sea blue bucket

I would keep doing these water changes. They aren't very effective in bringing your calcium down right now (you need 5 more changes until you drop below 500mg/L assuming nothing else consumes calcium and you don't dose any more calcium), but without these changes the imbalance would be even worse.

How are you maintaining magnesium and other elements?

 

[anthony1222]

Water changes should help to balance this. Also hobby level calcium testing is pretty unreliable. I would do your water changes and not worry with it very much.

I would keep doing these water changes. They aren't very effective in bringing your calcium down right now (you need 5 more changes until you drop below 500mg/L assuming nothing else consumes calcium and you don't dose any more calcium), but without these changes the imbalance would be even worse.

How are you maintaining magnesium and other elements?

i’m just dosing kalkwasser my tank is like 9 months old and im just starting out with corals

 

[Randy Holmes-Farley]

Kalk is a tiny bit overbalanced to too much calcium, but water changes typically limit the calcium rise. A value of 550 ppm is fine, but if you want it lower, reduce the kalk and use some pure alk supplement to replace it.

 

[anthony1222]

Kalk is a tiny bit overbalanced to too much calcium, but water changes typically limit the calcium rise. A value of 550 ppm is fine, but if you want it lower, reduce the kalk and use some pure alk supplement to replace it.

If 550 isn’t bad then I guess I should just keep it like that. Is kalkwasser a good method for a new tank or should I just go with 2 part

 

[Randy Holmes-Farley]

If 550 isn’t bad then I guess I should just keep it like that. Is kalkwasser a good method for a new tank or should I just go with 2 part

Yes, it’s a fine method. I used it for 20 years.

Some folks may also want to dose a trace supplement, such as Tropic Marin A and K.

 

[rishma]

I believe there is test error at play here. Your 10% water changes with Red Sea blue bucket are fine to keep calcium from rising too much.

Other than my typical skepticism about Trident and other calcium test kits, here is why I think the readings are erroneous…

Let’s assume your tank started with 420ppm calcium which I think is typical for Red Sea blue bucket. Kalkwasser adds about 5-10% more calcium than is consumed if you keep alkalinity stable. In a month, you are adding about 3-6 ppm more than is consumed.

To get from 420 to 550 ppm calcium would take 2-4 years with no water changes.

 

[EnterName]

Kalk is a tiny bit overbalanced to too much calcium, but water changes typically limit the calcium rise. A value of 550 ppm is fine, but if you want it lower, reduce the kalk and use some pure alk supplement to replace it.

Does this slight overbalancing apply to All for Reef as well?

Calcium hydroxide provides 2eq alkalinity:

Ca(OH)₂ → Ca²⁺ + 2 OH⁻
​

and so does calcium formate after the formate ion is oxidized to HCO3:

Ca(HCOO)2 + O₂ → Ca²⁺ + 2 HCOO⁻ + O₂ → Ca²⁺ + 2 HCO₃⁻​

I would have assumed calcium hydroxide and calcium formate are therefore more or less equivalent regarding alkalinity, but I don't know how differently OH⁻ and HCO₃⁻ will react in a reef tank.

Citation from your article:

 

[Randy Holmes-Farley]

Does this slight overbalancing apply to All for Reef as well?

Calcium hydroxide provides 2eq alkalinity:

Ca(OH)₂ → Ca²⁺ + 2 OH⁻
​

and so does calcium formate after the formate ion is oxidized to HCO3:

Ca(HCOO)2 + O₂ → Ca²⁺ + 2 HCOO⁻ + O₂ → Ca²⁺ + 2 HCO₃⁻​

I would have assumed calcium hydroxide and calcium formate are therefore more or less equivalent regarding alkalinity, but I don't know how differently OH⁻ and HCO₃⁻ will react in a reef tank.

Citation from your article:

Yes, AFR and kalk are identically over balanced to excess calcium. They match pure calcium carbonate and do not allow for magnesium replacement of some of the calcium.