Relativly low PH and 6 dKH consumption daily (kalkwasser + c02 scrubber + carbonate dosing)

[karsie]

Hi all,

I am wondering what my dosing, consumption, sensor values are telling about my tank health. I have some concern about the amount of dosing I do daily, consumption of the tank and still relativly low pH.

Some tank info:
165L/44G
Skimmer with C02 scrubber (on 24/7)
Mixed reef with great growth on all corals SPS/LPS
Coraline algea growth is substantial on glass
Glass in the sump is relativly quickly precipitating heaters and pumps as well, sand did precipitate once in just one corner.

Some parameters info:
temp: 24.7
pH: low 8.06 high 8.12 (calibrated today with both 7 and 10 solution on 25c/77f)
dKH: 8.6 consumption rising
Calcium: 461 consumption rising
Magnesium: 1460 stable

Some consumption info:
180ml/0.047G of carbonate daily
500ml/0.132G kalkwasser (not fully saturated)

Main question/concern:

How can it be that I have over 6dKH consumption daily, and still have a ph of only 8.11 with kalkwasser, c02 scrubber and carbonate dosing. Is it abiotic precipitation? But how is that possible with a ph of only 8.11 max?

 

[Randy Holmes-Farley]

Can you clarify how you are calculating the 6 dKH per day of alk addition?

I cannot tell what the carbonate solution potency is.

 

[Randy Holmes-Farley]

The kalkwasser is adding less than 0.4 dKH per day. How much lower depends on the potency.

 

[karsie]

Can you clarify how you are calculating the 6 dKH per day of alk addition?

I cannot tell what the carbonate solution potency is.

Sure, I use food-grade bi-carbonate and bake it for 75 minuts at 320f , then dose around 1.6KG/3.5 pounds to 10L/2.6G of water. Which should give me around 28ml/0.88Oz = 1dKH.

Edit: purity is 99.7%

 

[karsie]

The kalkwasser is adding less than 0.4 dKH per day. How much lower depends on the potency.

I use around 14G/3.3 teaspoons per 10L/2.6G kalkwasser

 

[Randy Holmes-Farley]

Sure, I use food-grade bi-carbonate and bake it for 75 minuts at 320f , then dose around 1.6KG/3.5 pounds to 10L/2.6G of water. Which should give me around 28ml/0.88Oz = 1dKH.

Edit: purity is 99.7%

That 1.6 kg that is dissolved into 10 L to make a dosing solution is weighed before or after baking?

 

[karsie]

That 1.6 kg that is dissolved into 10 L to make a dosing solution is weighed before or after baking?

Weighed before baking.

 

[Randy Holmes-Farley]

OK, so 1.6 kg/2.6 gallons = 615 g/gallon. That is 1.04 x the potency of my DIY two part, and so using this calculator:

Reef Chemistry Calculator

reef.diesyst.com

I calculate that adding 180 mL of it to 44 gallons adds about 5.9 dKH, so yes, you are adding close to 6 dKH per day.

That is excessive and is likely to to precipitation of calcium carbonate. Often that can be seen in hardening sand, and on pumps and heaters.

Do you observe any of those things?

FWIW, if you add carbonate and precipitate carbonate, there is no net pH boost to the system.

 

[karsie]

OK, so 1.6 kg/2.6 gallons = 615 g/gallon. That is 1.04 x the potency of my DIY two part, and so using this calculator:

Reef Chemistry Calculator

reef.diesyst.com

I calculate that adding 180 mL of it to 44 gallons adds about 5.9 dKH, so yes, you are adding close to 6 dKH per day.

That is excessive and is likely to to precipitation of calcium carbonate. Often that can be seen in hardening sand, and on pumps and heaters.

Do you observe any of those things?

FWIW, if you add carbonate and precipitate carbonate, there is no net pH boost to the system.

I did notice the hardening of sand in one part of the aquarium and my pumps and heaters percipitate rather quickly as well as the glass botom in the sump.

Your explanation sounds very logical as of why the pH can still be on the lower side with that amount of carbonate dosing.

What is the best thing to do from here? I thought of the following:
Stop dosing kalk,
Aim for 7dkh dkH (cutting the dose in half?),
Turn the skimmer of when a ph of 8.05 is reached

Would that be a go starting point?

Thanks so much!

 

[Randy Holmes-Farley]

This is my generic advice for such situations:

1. Stop all efforts to boost pH.
2. Stop dosing alk for a bit and let it decline.
3. Reduce pH by switching to a low pH alk mix like sodium bicarbonate, or a calcium organic such as Tropic Marin All for Reef.
4. Ensure magnesium is normal to high.
5. Keep organics and phosphate on the high side.

After a few days of not dosing alk, restart slowly, adding additives to a very high flow area so it mixes in fast.

 

[karsie]

This is my generic advice for such situations:

1. Stop all efforts to boost pH.
2. Stop dosing alk for a bit and let it decline.
3. Reduce pH by switching to a low pH alk mix like sodium bicarbonate, or a calcium organic such as Tropic Marin All for Reef.
4. Ensure magnesium is normal to high.
5. Keep organics and phosphate on the high side.

After a few days of not dosing alk, restart slowly, adding additives to a very high flow area so it mixes in fast.

Will do all of the above, thanks for the quick response and help. Very informative.

 

[karsie]

Quick update also for future readers, inmediatly stopped the c02 scrubber, halved the kalkwasser (250ml) and halved the bi-carbonate dosing (80ml). Ph Dropped to around 8 and dKH still stayed steady at 8.6 this morning (so seems like consumption is already dropping).

Just fully stopped the kalkwasser and halved the bi-carbonate dosing again (40ml). Tomorrow morning will do another dKH measurement and then fully stop bi-carb dosing for two days. Will report the findings later

 

[Randy Holmes-Farley]

Thanks for the update!

 

[karsie]

Update, fully stopped dosing carbonate and this morning dkh still was 8. Checking again tomorrow.

Randy, i got one question. Is the precipitation that is still in the tank going to "attract" the carbonate and calcium when starting dosing again?

 

[rtparty]

This is my generic advice for such situations:

1. Stop all efforts to boost pH.
2. Stop dosing alk for a bit and let it decline.
3. Reduce pH by switching to a low pH alk mix like sodium bicarbonate, or a calcium organic such as Tropic Marin All for Reef.
4. Ensure magnesium is normal to high.
5. Keep organics and phosphate on the high side.

After a few days of not dosing alk, restart slowly, adding additives to a very high flow area so it mixes in fast.

Randy, can you elaborate on point 5 please? I believe this will answer a question I have had for a while but haven't seen a concrete answer: Why do some fresh saltwater mixes precipitate and not store well yet they are fine in an aquarium?

 

[Randy Holmes-Farley]

Update, fully stopped dosing carbonate and this morning dkh still was 8. Checking again tomorrow.

Randy, i got one question. Is the precipitation that is still in the tank going to "attract" the carbonate and calcium when starting dosing again?

It will when fresh, and much less so as time passes and other things bind to the surface and make it not attractive to more calcium carbonate precipitation. That’s the reason to slow dosing for a few days.

 

[Randy Holmes-Farley]

Randy, can you elaborate on point 5 please? I believe this will answer a question I have had for a while but haven't seen a concrete answer: Why do some fresh saltwater mixes precipitate and not store well yet they are fine in an aquarium?

Organics and phosphate are well known in the literature to block precipitation of calcium carbonate by making the surface not look like a good seed crystal for more precipitation. That’s how magnesium works as well. I think even whole bacteria can serve this purpose.

Yes, things in 5 are, IMO, a big reason why raw artificial seawater is much more prone to precipitation than is reef tank water at the same basic values for alk, pH, and calcium.

I did an experiment years ago where I found I could boost the alk and pH in a test tube very high using ESV alk part plus raw salt water, plus a polymer known to bind to CaCO3 surfaces (sodium polyacrylate). The same could not be done without the polymer.

 

[karsie]

Thanks for the extra details. Is it also that a higher salinity increases the chance of precipitation?

Update:
Ph is around 8 high 7.8 low
Dkh is 6.8

Dosed a little bit of bi carbonate to keep it around 7.

 

[Randy Holmes-Farley]

Thanks for the extra details. Is it also that a higher salinity increases the chance of precipitation?

Update:
Ph is around 8 high 7.8 low
Dkh is 6.8

Dosed a little bit of bi carbonate to keep it around 7.

No, higher salinity is complicated, but probably reduces precipitation. There are several effects in different directions.

 

[karsie]

No, higher salinity is complicated, but probably reduces precipitation. There are several effects in different directions.

Thank you, can I start dosing carbonate again or must it be bi carbonate?