Tank won't hold phosphates

itsnicholas · Feb 1, 2026

Hello, I have a 75 gallon tank that is SPS dominated. I have been struggling to keep my phosphates above 0.02 or even 0.00. I dose NeoPhos pretty much daily at this point, and I feed the fish pretty heavy. 2 days ago, I tested my phosphates and it was 0.05. Today, when I tested phosphates again, it was 0.00. I tested 3 times. All say 0.00.

How can I hold phosphates? I haven't had my skimmer running in months. Also, my tank Alkalinity jumped from 8 to 10 almost 2 weeks ago which caused tip burn. All parameters have been stable since then (little backstory).

Any advice is appreciated!

Dan_P · Feb 1, 2026

itsnicholas said:
Hello, I have a 75 gallon tank that is SPS dominated. I have been struggling to keep my phosphates above 0.02 or even 0.00. I dose NeoPhos pretty much daily at this point, and I feed the fish pretty heavy. 2 days ago, I tested my phosphates and it was 0.05. Today, when I tested phosphates again, it was 0.00. I tested 3 times. All say 0.00.

How can I hold phosphates? I haven't had my skimmer running in months. Also, my tank Alkalinity jumped from 8 to 10 almost 2 weeks ago which caused tip burn. All parameters have been stable since then (little backstory).

Any advice is appreciated!

Put the skimmer on. It has nothing to do with phosphate depletion. Your system is consuming phosphates. Add phosphate. You might want to switch to a greater strength DIY phosphate solution. I assume you aren’t using GFO. If you are growing macro algae definitely increase phosphate addition.

blackgate · Feb 1, 2026

When I struggle with low phosphate, it’s always Reef Roids to the rescue, you feed heavy with those and your phosphates will rise!!

etcee · Feb 2, 2026

I wouldn't care about the number. heavy in heavy out.

zheka757 · Feb 2, 2026

Add more fish! Lol, I use to have your problem years ago, back when I had my fish small, now my 11 tangs are big and fat, and I cant keep my phosphates down