No Algae Anywhere, but green tint to water?

[PotatoPig]

I’m running a FOWLR tank with room lighting (room lights are over tank so fish show up nicely anyway l, could probably improve with actual aquarium lights, but fine for now.

I have a refugium, with rocks (copepod farm), and a grow light that’s turned on overnight.

I can’t see a single speck of algae on the glass or rocks, of any description, anywhere, not even on the highest rocks directly under the grow light.

What I can see is a noticeable green tint to the water… I first noticed this a little after adding a frozen food that was highly green colored, but I’m not sure that’s the source as the tint has persisted for a while now. It doesn’t seem to be getting worse, but it ain’t getting better either.

Any idea what’s causing this or what I can do to cut it down?

 

[HawkeyeDJ]

Are you feeding your copepods phytoplankton? That could be the source of the green tint. Also, a high quality activated carbon may eliminate it.

 

[Tired]

That's algae /in/ the water. What does your refugium look like, and what are your parameters? Specifically, nitrates and phosphates.

 

[PotatoPig]

Are you feeding your copepods phytoplankton? That could be the source of the green tint. Also, a high quality activated carbon may eliminate it.

No, no supplemental feeding beyond whatever detritus makes it their way. The fish food includes stuff like spirulina that I know pods eat, among other stuff.

That's algae /in/ the water. What does your refugium look like, and what are your parameters? Specifically, nitrates and phosphates.

I realized I should have e tested before posting and am out now, I’ll follow up with a photo and parameters.

 

[PotatoPig]

That's algae /in/ the water. What does your refugium look like, and what are your parameters? Specifically, nitrates and phosphates.

So I’m not 100% on interpreting the colors, and am assuming I’m supposed to look at the tubes side on rather than down.

I make:

Phosphates: 0.25
Nitrate: ~5

Included pictures of the sump, the goals of this are almost entirely for pod production, and it seem to work. The water enters the middle chamber at the base, has a 2” free flow area under the rocks and diffuses up through them sending countless numbers of them into the return chamber and then their eventual doom in the DT. But as you see, not a hint of algae even right under a grow light.

Have plans for a skimmer, but for the time being the nutrients sure seem on the low side so it hasn’t been an immediate concern.

Weirdly, photos through the tank don’t show the tint that’s very clear, albeit not horrific, when looking at it. Like the camera is color correcting.