How long does dry rock tend to soak up phosphates?

[MarsReefer]

I’m having trouble keeping my phosphates above 0. Nitrates are pretty stable at 4-5 ppm so I assume my rocks and/or sand is sucking up the extra phosphate.

I’ve been dosing 0.02 ppm phosphates every few days to keep it above 0, but it drops back down pretty quick. How long does it usually go on until it saturates?

 

[Randy Holmes-Farley Verified Community Expert]

Depends on how fast you add it and how much surface area there is. It binds until it has as much as is in equilibrium with the water.

I’d suggest upping the daily amount dosed to 0.05 ppm until you start to see some in the water. That amount is still lower than you likely add via foods each day.