Lowering Alkalinity with sodium bisulfite

miller75 · Nov 30, 2025

Randy Holmes-Farley said:
Alk can rise from several sources:

1. Falling or dosing nitrate. Its consumption adds alk.

2. Slow dissolution of rock and sand down inside it where pH is low. This generally always happens at a low rate and is lost in larger demands, but in a no demand tank, can be significant.

3. Top off with tap water that has alk.

4. Water changes with a mix that has higher alk than the tank.

5. Additions via products that may have alk you are not aware of.

6. Dosing pump issues.

7. Recipe for alk solutions not followed correctly.

8. Finally, maybe it sn’t rising: it’s a testing problem.

I have eliminates most of these which is why I am thinking sand

1. I have had no significant drop or rise in nitrate

2. This is what I am thinking, I have virtually no demand in the tank

3. I am using RODI, I have just replaced all the filters and DI just in case

4. Same salt and I have tested fresh mix at 8.2 on the same Hanna I am using to test the tank

5. Apart from food I have just started dosing a bit of nopox

6. Nothing connected except nopox

7. Not dosing any

8. I am using Hanna and KH Director, I will get a Salifert to triple check

My initial though was my salinity but I have recalibrated my probe and refractometer and its at 34.8, then thought it could be my salt but that tests fine with the same Hanna I am using for the tank, finally I thought it could be the Seachem clarity I was using but its still rising after I stopped using it about 6 weeks ago.