Do Green Star Polyps consume phosphate excessively?

divetoday · Jul 17, 2022

Okay, okay. I know all corals consume nutrients, but I have a strange situation. I have a 30 gallon BB cube that is about 40% covered in GSP. There are 4 fish (cow fish, damsel and two percs) in addition to some RBTA and zoas. The Hanna checker reliably tells me this tank is at 0.00 phosphate. I can move the nitrates on the tank by increasing feeding but not the phosphates. I have another tank I use the same checker on and get results in the expected 0.05 to 0.1 range so I don’t think it’s the checker or the reagent. I have heard that some people use Xenia in large refugia for phosphate control, but not GSP. Has anyone else seen this reported?

Randy Holmes-Farley · Jul 17, 2022

It’s not the green star polyps.

It may be any bare calcium carbonate surfaces, such as rock or sand. It can bind a tremendous amount of phosphate before reaching equilibrium with the water.

divetoday · Jul 18, 2022

Thanks Randy. It’s an established tank, bare bottom with some live rock but not a ton.

Tired · Jul 18, 2022

Get that phosphate up! 0 phosphate will kill photosynthetic organisms. You generally want a minimum of 0.03ppm at all times.

The GSP isn't helping matters. Fast-growing corals are good at using up nutrients.

EricR · Jul 18, 2022

Interesting. I guess I'll go with what Randy said but I was thinking "maybe."

My phosphates seemed to plummet when I added 7 zoas.
Could be due to half my rock being dry rock when I did tank transfer 8 months ago but I didn't notice phosphates fall until I added zoas a couple months later.

Tired · Jul 18, 2022

7 zoas wouldn't plummet phosphates in anything larger than a shot glass.

(Edit: assuming you meant 7 polyps or 7 frags, not 7 large colonies.)

Randy Holmes-Farley · Jul 18, 2022

What I meant was that gsp is not taking up unusually large amounts of phosphate, but I agree it can be a fast grower and will thus take up N and P in proportion to it’s growth.