No chaeto growth in reactor

[penguin_free]

About a month ago I started up an algae reactor (the larger skimz model from BRS, 12hr light cycle) in the sump of my 120gal, hoping to displace the gfo and vinegar dosing, and allow for a little NO3 & PO4. I dosed a couple teaspoons of iron supplement at startup, just figuring what can it hurt?
Over the first month I've let PO4 rise to about 0.1ppm and NO3 rise to about 10ppm, and when I checked the reactor last friday, the chaeto was mostly still alive, but there was somewhat less than I started off with.
On the upside, I did notice a little caulerpa had grown in there. I had not noticed any caulerpa in the chaeto ball I started with, so maybe that'll grow better...
I have adjusted the vinegar dose up a little to bring the NO3 back down to 5ppm, and ran some gfo for a couple days to pull the PO4 back down (yesterday's check read 2ppb N though, I let that run a little longer than I should have)
Is there anything I'm obviously missing here?

 

[Xclusive Reef]

how long has the tank been running? what kinda lights do you have over your tank? and last what is in your tank fish, corals etc?

 

[penguin_free]

It's been running around 3 years now, lighting is all T5 (6 54w ati blue plus / 2 54w ati coral plus). I'm running a pretty heavy bioload; 4 tangs, 3 wrasse, 2 dwarf angels, a copper band butterfly, a mandarin, and a springeri goby.
Corals are a mix of softies and lps; various zoos, green sinularia, xenia and cesspitularia, elegence coral, torch colony, green goniopora, branching hammer. Yes, it takes a good reactor load of GAC to keep those coexisting, lol