Phosphate reduction not working.

CopperFish · 2026-11-15T11:27:03-0500

I had to swap out my tank about 4 months ago (due to impending seam failure) and replaced my almost nonexistent sand bed with a new 1 1/2 to 2 inch sand bed using CaribSea special Grade sand. Ever since, my phosphates have been hard to manage going from an average of .05-.1 to now .68. I tried adding copepods, using lanthium chloride, RowaPhos in an fluidizer and water changes but no matter what I do my phosphates rise back up into this range. One theory I researched is that my rocks are leaching phosphate as they have been in the system for four years since I started the tank, but having a new sand bed might have changed the balance and now phosphate is leaching out of the rocks. Any insights or suggestions would be great, my parameters are below. All corals look healthy except my two Goniapora, not sure why they are struggling. Could be some alk swings or maybe the increased phosphate levels? I guess I'm trying to figure out if this is just my new norm and should be OK with it or if I should continue trying to reduce my phosphate levels to the .05 to .1 range. I just sent in a new ICP test to see if something else is off and should have those results in about a week.

Calcium: 399
Magnesium: 1301
Alk: 7.89
Salinity: 1.26
Nitrate: 3.8
Phosphate: .68
Temp: 78

142 gallon total system. Dosing 40ml/day All for Reef and part b for alk as needed. 20% water change every 2-3 weeks and I use Tropic Marin Pro Reef salt. I feed once a day rotating between frozen brine/mysis and pellet food. I feed the corals twice a week, once with Reef Roids and once with Red Sea AB+.

Randy Holmes-Farley · 2026-11-15T11:41:25-0500

Copepods won’t noticeably impact phosphate, but GFO and lanthanum will if you use enough. That said, it can take far more to reduce phosphate in a reef tank than in a bucket due to the need to strip it from the rock and sand. Calculators and recommendations are generally only useful to prevent massive overdosing.