Help with a new tank with very high alkalinity demand

[Reef-Engineer]

Hi All,

Question for the chemists in the gang, and thanks in advance for your time.

I have a 300g reef, probably about 3 months old with the rock cycling for another 6 months before that. Three fish, few tester corals, a few snails/hermits.

Current Tank Parameters:
ALK: 6.9dKh (tested with Hanna and a calibrated Trident)
CA: 380ppm (tested with Hanna and a calibrated Trident)
Mag: 1425 ppm (tested with calibrated Trident)
SG: 1.025 (tested with refractometer, calibrated salinity probe, and milwaukee tester)
Nitrate: (was zero for a long time, just added NeoNitro after last few days, hoping it is 2-5ppm now, testing shortly), tested with Hanna
Phosphate: 0.01 (was also zero for some time, just added a bit of NeoPhos too, just to raise it a touch), tested with Hanna

The question: I wanted to start the tank on Kalkwasser, and then add a CARX once the demand was too high. I thought that would be waaaay down the road when it was full of coral, but the tank is relatively new, with almost no coral, and the demand for ALK is very high. I started with 1.5L/day of Kalkwasser and am up to 4.5L/day and my ALK which was stable for some time at 7.3dKh has started to fall again (now at 6.9dKh).

I see no signs of the substrate (reborn and aragonite sand) solidifying, I see no obvious precipitate anywhere. Is it possible that a new tank would consumer 4+ Liters of kalk (mixed to 2TSP/Gal) and still not have enough ALK to stay stable in the 7.5 dKh range? What am I missing?

The tank only evaporates a gallon or so of water per day, so I am already almost matching my evaporation rate with Kalk, and I have minimal SPS.

My guess was tube worms growing skeletons and coralline algae growing, but I really don't see that much on the rocks. When I started the NeoNitro, the ALK started to drop again suggesting that whatever is consuming ALK also wanted Nitrate.

What am I missing here?

Tank pic for fun:

 

[boacvh]

I have a 240 and experienced something similar. Very large alk consumption at first that after that slowed down considerably. I chucked it to Coraline growth, which in that phase was massive. Once it covered everything my alk consumption dropped so I blamed it on that. But TBH no clue what it was. Also, if you are doing water changes I'd say check the alk in the new water. Other that that, not sure what it could be.

 

[Reef-Engineer]

I have a 240 and experienced something similar. Very large alk consumption at first that after that slowed down considerably. I chucked it to Coraline growth, which in that phase was massive. Once it covered everything my alk consumption dropped so I blamed it on that. But TBH no clue what it was. Also, if you are doing water changes I'd say check the alk in the new water. Other that that, not sure what it could be.

Thank you for the data point!

I was thinking coraline as well, just don't see a ton of it so was surprised. I plan to raise my CA to 420+ and then just continue to increase the ALK dosage to keep up with the "mystery demand", just confused as to why this is occurring.

 

[Randy Holmes-Farley Verified Community Expert]

Abiotic precipitation is always happening and can happen more in newer tanks before all calcium carbonate surfaces are covered with stuff.

But I’d challenge the very high demand claim. You are adding less than 0.5 dKH per day.

 

[Reef-Engineer]

Abiotic precipitation is always happening and can happen more in newer tanks before all calcium carbonate surfaces are covered with stuff.

But I’d challenge the very high demand claim. You are adding less than 0.5 dKH per day.

Thank Randy. I’ll stay the course.

Agreed when I put it in terms of dKh it doesn’t sound so excessive.

i just retested alk with hanna, got 7.2 so at least hanna repeatable, trident measuring a little low.

Also tested kalkwasser effluent 3 times (full strength, 1/2, 1/4 strength) all over 20dkh which checks out because saturated kalkwasser has an alk north of 110dkh i think.

I think ill raise my calcium a bit, keep dosing kalk as i cam, and see if the consumption slows as all surfaces are coated.

 

[Reef-Engineer]

Randy or others, wanted to check back in. My kalkwasser dosing is 4500ml/day between 0300 and 0900. Over the last several days my alk has slowly stepped down from 7.4dkh to 6.5dkh. Confirmed results from Trident with Hanna.

Magnesium is 1440 and CA has been rising and there is disagreement between trident which says 394 and hanna which says almost 500ppm.

So it seems like my CA may be rising and alk continues to drop.

On two occasions i have dosed soda ash solution to bring the alk back up into the 7’s.

Any guesses? My coral load is still a few small frags. My water volume is likely ~325g with rock/sand/reborn in tank.

Still no evidence of excessive precipitation. Only odd thing is that my skimmer goes NUTS whenever it is on.

Corals seem happy if a bit pale (nutrients nitrate 9ppm phosphate 0.02ppm).

 

[rishma]

I cannot help other than to say I dosed a lot of kalk when my tank was new and the apparent alkalinity demand seemed high considering few consumers. I never did figure out what was happening but figured it was related to Randy’s comments on precipitation and/or the nitrogen cycle. I did not see a lot of visual evidence except a little clumping of sand. Alkalinity consumption settled way down after a couple of months based on my memory.

 

[Randy Holmes-Farley Verified Community Expert]

There are not many ways that calcium is significantly and rapidly rising when alk is falling. Given the test variables in calcium, maybe it’s the Hanna that is off.