High phosphate, low nitrates???

[Scrubber_steve]

Coming to think about it, it all started when I cut about a 1/2 or a maybe a 1/4, I don’t remember, out, cause it was getting a bit huge. After that now that I think about, it’s when I started reading a bit higher PO4....

cutting the algae stresses it & this causes it to leech exudates for maybe 15 minutes. The exudates will contain phosphate. How much of an effect this might have I don't know, & I don't know how often you cut the chaeto. But a way around this is to cut off the excess, & for 15 minutes leave the remaining chaeto to soak in a separate container of tank water before putting it back in the fudge.

 

[Sirlurkzalot]

Depending on the rock you used you might be leeching phosphates from your rock (I had this problem). I found running a refugium and a good quality skimmer cleared this right up. Everything has now balanced out (except for my bubble algae outbreak from a bad frag - dealing with this now).

 

[BeejReef]

Have had the same struggles balancing N and P in a young tank.

How big is your fuge relative to your tank? I would guess that you need more nitrate to power your fuge as well.
Another thing to look for is the health of your macro. If big chunks are shaded or there isn't much flow, it can start to give N and P back to the tank. In my case, I found an inch thick layer of dead brown chaeto sort of coating the bottom of my fuge chamber, blended in with my rubble rock. Siphoning all of that out absolutely crashed my N and P. Tank was not happy. If you find similar, I'd suggest slow and steady removal.

 

[Scrubber_steve]

Yeah, that was my first thought, was using salifer to test and those shades of blue confuse the heck out of me, so bought a hanna checker and boom, .36, .37,.38...

Is that a Hanna H1774 ?
Just read this from Lasse "Take a closer look at HI774. However - the Hanna checker not always show you the truth in this low range. I have one that show 0.12 ppm when TRITON says 0.038 ppm PO4."