Acceptable phosphate levels for fish as opposed to coral?

[Oceansize]

I understand, according to some of Randy's articles that I've read, that the optimum phosphate level for coral is 0.03 ppm. I'm curious if there is an appropriate level for fish, or rather, a maximum acceptable level for fish. Specifically a purple tilefish.

Until yesterday, I've been testing my phosphates using the API kit which I understand is not high-enough resolution to be of any use. I barely got any color change whatsoever, I would have to say the color was closer to a reading of zero than it was to the next highest reading of 0.25 ppm. But without a better test kit, the best I've been able to determine regarding my phosphate level is "less than 0.25 ppm" which doesn't really help. Since my coral has been doing fine, I haven't worried about it, apart from resolving to get a better test kit once I run out of reagent for the API kit.

Then this weekend I noticed one of my favorite fish was not looking good, and neither has my feather duster worm. With all other parameters checking out, I decided it's time to stop procrastinating and get a proper phosphate test kit, and I ended up ordering the Hanna Checker for Phosphate online.

With the fish continuing to decline, rather than wait for the kit to arrive before deciding on a next course of action, I immediately performed a 35% water change.

The very next day after I did the 35% water change, the phosphate checker arrived, and my reading is 0.13 ppm.

I know that is higher than the recommended level for coral and so I know that phosphate export is the next challenge for my tank that I need to figure out. Skimming + GAC 24/7 + UV is not cutting it, at least not without more frequent water changes.

In the meantime, however, I ended up losing the fish despite the water change. I'm still trying to identify the culprit if possible, and trying to eliminate elevated phosphate levels as the reason.

So the question is, understanding that my phosphate was 0.13 AFTER a 35% water change, is it possible that my phosphates are/were enough to harm my fish? Phosphates were never an issue when I was freshwater, I'm not used to worrying about phosphates as far as my fish are concerned, only my coral, so this is uncharted territory for me.

 

[Randy Holmes-Farley Verified Community Expert]

While I do not know about that fish in particular, I've not heard that phosphate is a problem for fish and some fine reef tanks have phosphate as high as 1 ppm without apparent fish issues.

 

[Oceansize]

Thanks Randy. As long as I've got your attention, do you have any thoughts on my running GAC constantly? Years ago when I started out with a freshwater tank, my trusty LFS guy sold me a canister filter and told me to run GAC in it all the time as a way to prevent disease. This was before the internet, I had no reason to doubt him, and I never had any issues that I'm aware of.

But now that I've gotten into reefing and have encountered a lot of advice on the internet, I notice that people frequently remark that they run GAC only part of the time, or "when necessary." Which possibly implies that there are reasons against running it all the time, and/or that it is generally used in more specific situations than mine.

I am in the habit of changing it out every month, but I'm just curious if there's a reason why I shouldn't be using it all the time as I have been. It was only recently that I encountered one of your articles extolling it's virtues as a phosphate limiter which excited me (I was only using it as a general precaution against disease), but so many people mention using it only temporarily, it makes me wonder if I shouldn't be using it so much.

Thanks again,
Barry

 

[Randy Holmes-Farley Verified Community Expert]

I don't think it helps with most diseases, but I run GAC (ROX 0.8 from BRS) 24/7. I'd be careful about nonacid washed GAC (possibly contributing to HLLE in tangs), but the ROX is a good choice.

It is a good way to export organic matter and reduce yellowing in the aquarium.