New Tank High Alk Consumption

[rdballard]

I set up a new tank about a month ago and can't for the life of me figure out why it's consuming so much alkalinity.

The tank is 150g with a 35g sump. I previously had a 55g and the rock and corals from that went into this tank. I added 120lbs of new sand and a lot of new rock as well. None of the corals are big enough to explain the alkalinity consumption.

Alk is 8.15, calc is 420, mag is 1350, phosphates are .06, nitrates 5-10, and pH is around 8.

Without dosing, the tank is consuming about .45dkh per day. I'm dosing 120ml of soda ash at 1.5cups/gal to keep it from dropping.

What's going on here and how can I fix it?

 

[Randy Holmes-Farley Verified Community Expert]

Bare rock and sand can act as seed crystals for precipitation of calcium carbonate. That is likely adding to the demand. You will have to let it get coated in phosphate, organics, bacteria, etc, and meanwhile slow down the precipitation.

Once it starts it becomes self sustaining since seawater is supersaturated in calcium carbonate.

This is my generic recommendation for excessive precipitation issues (such as hardening sand):

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.