Nutrients too low?

[Randy Holmes-Farley Verified Community Expert]

I have had the same exact issue. Careful soon your tank will find equilibrium and your nutrients will shoot up drastically So I think this issue you have is the result of dry rock. I have had many tanks over the years. One thing I've noticed is rock works like a sponge it's collects phosphate or if you use old live rock in a new system it will release phosphate. It all depends. Eventually when bacterial levels reach a favorable level and your rock is fully organic absorbed the tank will balance out or at least be more easily dialed to a desired level I couldn't keep an acro alive for over a year with dry rock and now my tank is full of thriving acro.

I think at least part of the issue is unrelated to bacteria or organics.

Bare calcium carbonate surfaces are known to bind very large amounts of phosphate from seawater. It can be the equivalent of many ppm in solution, but reversibly bound to the rock surface.

The higher the phosphate concentration in the water, the more binds.

So when dosing at very low levels, it can take far more dosing than expected tog et levels up to where you want them.

Likewise, when water levels are high and a lot is bound, it can be frustratingly slow to remove it all because it seems to keep coming back into solution.