Phosphates in Fish Only Tank

Dustinryan2010 · Oct 9, 2018

How important are they? Just purchased a Salifert test kit, what levels should I be aiming for with a FOWLR system?

Reefing Madness · Oct 9, 2018

FOWLR? Don't worry about them.

WWIII · Oct 9, 2018

I don't think phosphates are important at all personally in a fish only tank, other than keeping them on the low end to inhibit algae growth. I had fish only systems I never tested phosphate in for years without issue. Granted we didn't really have that great of phosphate test kits back then.

I would aim for under 1ppm. Ideally under 0.1 ppm. That will ensure the water quality (as far as phosphate) is good and help to limit algae growth.

Dustinryan2010 · Oct 9, 2018

Reefing Madness said:
FOWLR? Don't worry about them.

dang wasted money lol. Thanks for the reply!

piranhaman00 · Sep 4, 2020

Bump.

PO4 in fish only? I am approaching >2.0ppm, not much algae growth because of light schedule. Is this problematic to fish?

excell007 · Sep 4, 2020

I have 90G with 20G sump FOWLR for 15 years and only measured salinity and PH. I have no trouble keeping fish alive, I probably lost less than 15 fishes since 2005, my first 2 inhabitants(purple and sohal) died just 2-3 years ago. Yellow tang is the only fish I can't keep alive for more than a few months, lost 3 of them and never tried again. Early this year I decided to convert it to a reef tank and started measuring, API nitrate and Hanna phosphate ULR can't even measure the level. I have to dillute the sample to be able to guage the level. so last March my nitrate is >300 and phosphate >4. I've been slowly reducing it by 30% weekly water change and now nitrate is less than 10 and phosphate is 2, phosphate is harder to reduce because the rock absorbs it, but I am getting there. I have 11 fishes in the tank and did not loose any of them with this reduction of prameter. Still no LPS or SPS but I think I'll be able to add them in a couple of months. But as I found out early on, in this hobby no tank is the same.

piranhaman00 · Sep 4, 2020

excell007 said:
I have 90G with 20G sump FOWLR for 15 years and only measured salinity and PH. I have no trouble keeping fish alive, I probably lost less than 15 fishes since 2005, my first 2 inhabitants(purple and sohal) died just 2-3 years ago. Yellow tang is the only fish I can't keep alive for more than a few months, lost 3 of them and never tried again. Early this year I decided to convert it to a reef tank and started measuring, API nitrate and Hanna phosphate ULR can't even measure the level. I have to dillute the sample to be able to guage the level. so last March my nitrate is >300 and phosphate >4. I've been slowly reducing it by 30% weekly water change and now nitrate is less than 10 and phosphate is 2, phosphate is harder to reduce because the rock absorbs it, but I am getting there. I have 11 fishes in the tank and did not loose any of them with this reduction of prameter. Still no LPS or SPS but I think I'll be able to add them in a couple of months. But as I found out early on, in this hobby no tank is the same.

Wow! Well nitrate is toxic to fish in high levels and >300 is the highest I have seen haha! My nitrate is <50ppm, not worried about that. I just cant find anything in relation to PO4 levels.

JumboShrimp · Sep 4, 2020

Based on you post I just tested the Phosphate level in my FOWLER. Last time I tested (6 months ago?), it was off the API-chart— Higher than 10.0 ppm. It is again now. Fish seem fine, as always, but I do have a Cyanobacteria problem (bare-bottom tank). Take this for whatever it adds to the conversation. Best wishes!

piranhaman00 · Sep 4, 2020

JumboShrimp said:
Based on you post I just tested the Phosphate level in my FOWLER. Last time I tested (6 months ago?), it was off the API-chart— Higher than 10.0 ppm. It is again now. Fish seem fine, as always, but I do have a Cyanobacteria problem (bare-bottom tank). Take this for whatever it adds to the conversation. Best wishes!

Just what I wanted to hear actually, thanks! I also have some cyano, hair and bryopsis, but I dont care that much. Ill keep monitoring, thank you for your input :)

excell007 · Sep 4, 2020

piranhaman00 said:
Wow! Well nitrate is toxic to fish in high levels and >300 is the highest I have seen haha! My nitrate is <50ppm, not worried about that. I just cant find anything in relation to PO4 levels.

Been neglecting it since the purple tang died, just topping off and checking salinity. It was darker than the darkest color on the test strip which is 200 and darker than the darkest color on the API chart which is 160, so I dilluted the sample, 50% RODI, and it was barely lighter than the 160 color. It took me 10 weekly water changes to bring it down to <10