Can't raise Phosphates

johninja · 2026-07-27T10:12:12-0400

Hi all,

Tank has been filled up start of Dec 2025, cycled for 40 days and got some shrooms and sarco, and 2 clowns and cleaner shrimp. Few Trochus snails and 2 nassarius.

My phosphates were 0,8 at the start so I added GFO and took it out after bottoming out (about 2 weeks). This was in January and ever since only 1 time I had 0.03, it's 0.00 (using hanna checker).

I had a GHA problem for months, it's now gone, and yet phosphates are still 0.00.

Params:
Alk 7.3-7.5
Ca 350-400
Mg 1230
Nitrate 2.5

I've been adding phosphates (aquaforest) 2ml daily with no success.

Any help is appreciated before dinos come.

Thanks!

Gumbies R Us · 2026-07-27T10:25:30-0400

What are you feeding your tank? (food-wise)

What kind of filtration do you have?

How frequently are you doing water changes?

Anything else you are dosing?

EnterName · 2026-07-27T11:16:48-0400

In natural coral reefs phosphate levels are very low so even if the HannaChecker shows 0.00ppm it doesn't have to cause any issues. If low phosphates (or overall nutrients) are actually the cause of dinos or rather a symptom appears to be a controversial topic.

I personally dose phosphate daily multiple times with a dosing pump to keep it above 0.00ppm as "safety measure". Not doing this causes minor dinoflagellate growth in my tank (repeatedly tested over the course of 2 years). The following DIY recipe is a far cheaper solution than buying pre-mixed products, and you can even scale it's concentration based on the tank volume: https://www.reef2reef.com/threads/diy-phosphate-dosing-recipe.1109919/

If phosphate keeps staying below detectable levels, add more until you find the sweet spot that doesn't increase phosphate further, but allows for detectable phosphate levels. I highly recommend testing daily (at the same time) for a while until you have found the correct amount. Increase the dosage in small amounts as sudden phosphate spikes seem to be correlated with sudden tissue necrosis in some corals or at least a negative reaction (e.g. staying closed).