Alk consumption on tank without corals

KGscv · May 28, 2025

I have a newly setup 120g tank for about 2 months. DT has special grade sand and dry rock seeded it with tbs sand and premium live rock in sump. Tested alk on 1 month mark and my alk was low 5s. So i started dosing with afr. Right now im dosing about 30ml a day with alk ranging 6.8-7.2 tested with hanna and salifert. I see specs of coralline in powerheads and in the rocks. Is this normal amount if alk consumption on and empty coral tank?

Tyberzann · May 28, 2025

Alk is consumed during the conversion of ammonia to nitrite to nitrate so expect to see a drop during cycling.

It may also be worth checking to ensure you salinity readings are correct on new salt mixes to ensure you introduce new water at the correct Alk level.

I have found AFR to be much better at maintaining an ALK level rather than increasing it, but an empty tank post cycle doesn't usually consume massive amounts of Alk.

KGscv · May 28, 2025

Tyberzann said:
Alk is consumed during the conversion of ammonia to nitrite to nitrate so expect to see a drop during cycling.

It may also be worth checking to ensure you salinity readings are correct on new salt mixes to ensure you introduce new water at the correct Alk level.

I have found AFR to be much better at maintaining an ALK level rather than increasing it, but an empty tank post cycle doesn't usually consume massive amounts of Alk.

Tank cycled in 10 days. Salinity is corrct and tested with milwaukee and refractometer. Do you think its being consumed by the coralline thats growing on the rocks?

Tyberzann · May 28, 2025

Coralline will consume some alk, the amounts really depend on how prevalent the coralline is. I would be shocked if it was consuming 25mls worth of AFR.

Randy Holmes-Farley · May 28, 2025

What else is in the tank?

KGscv · May 28, 2025

Randy Holmes-Farley said:
What else is in the tank?

No corals, about 3 lbs of tbs premium live rock and 7 lbs of live sand in sump. 8 fish, bunch if cuc. Thats about it.

Randy Holmes-Farley · May 28, 2025

KGscv said:
No corals, about 3 lbs of tbs premium live rock and 7 lbs of live sand in sump. 8 fish, bunch if cuc. Thats about it.

Snails? They use alk. So will other creatures on the rock, including coralline. As mentioned above, rising nitrate depletes alk.

In any case, I’d just supplement as needed.