Phosphate reduction question (negligent rapid reduction)

[Chunky94]

What is going to happen and what can I do? Phosphate dropped from .44 to .06 overnight
I installed a gfo reactor I used 9 tbs meant to use 3, removed half of my sea lettuce and did a 25-30 % water change at the same time the night before. It's a biocube 32 with a mix of lps and soft coral.

 

[Randy Holmes-Farley Verified Community Expert]

I'd turn off the reactor and measure phosphate later today. It might pop right back up.

 

[Chunky94]

I'd turn off the reactor and measure phosphate later today. It might pop right back up.

It came back up to .2 should I continue to run the reactor or at this point will my sea lettuce and water changes maintain this level?

 

[Randy Holmes-Farley Verified Community Expert]

It came back up to .2 should I continue to run the reactor or at this point will my sea lettuce and water changes maintain this level?

I'd follow it a bit and see what happens, but probably keep the reactor running.

 

[Chunky94]

I'd follow it a bit and see what happens, but probably keep the reactor running.

Could I get your recommendation on how much gfo to use. It's a biocube 32, with 2 clowns, scooter blenny, lawnmower blenny, six line, tiger pistol shrimp and ywg. I have lps and soft corals plus a rock flower anemone. Im probably overfeeding the tank as well but trying to keep the scooter blenny happy

 

[FishTruck]

As long as it does not drop to 0.0 you are fine. It's not like Alkalinity... the sudden drops don't hurt anything so long as you don't put it down to 0.0. You can't really get steady state until the phosphate is pulled out of the rocks, which will take some repeated dosing.

Follow it a bit like Randy said, and I'll bet it will go back up to .44 pretty soon.

Best way to figure the dose of GFO is trial and error on your own system with a consistent product. Usually, starting with 1/2 the manufacturers recommended amount.

Here is a calculator. I use this, then divide it by 2. Trial and measure before and after. Then with experience you will know how much to use to drop your phosphate a certain amount.
https://www.bulkreefsupply.com/reef-calculator/gfo-calculator
Plan on this being a weekly task for awhile, then a monthly task once the rocks are finally depleted of phosphate. Or, eventually, another nutrient export method is introduced.

Another method based on your own data....
If it goes back to .44 - use half as much as you did last time and measure the before and after (4.5 tbs).

Or.. if the phosphate stays at .2 - use 1/4 as much as last time (2.25 tbs). Target I assume is .05 to .1.