Prodibio is on the 15 days schedule, I was hoping 1 vial of everything except the yellow food stuff would be sufficient since I'm so close to the 50 gallon cut off. Doubling the dose puts it at $40/month, too rich for me unless I just do the bioptim/biodigest and dose the iodine and strontium monthly.

I've thought of an Algae scrubber since the chaeto isn't doing so hot. I'll have to do some reading as the only way I could manage it would be to tie it into my return so I wouldn't need yet another pump in the sump, It'd also have to be one sided due to the way things fit.

Lighting is AI Sol's so I doubt that's contributing to the problem.

You say 5g every 2 months? That's not frequent. I would expect nutrient excess at that.
I would increase water changes to more water, more often...

Crap, I meant to say WEEKS... 5 gallons every two weeks :) but maybe had twice a month stuck in my head as I was typing!

If space is a issue for a algea scrubber try using your overflow lines to supply water to the screen. Of coarse the would be on sided.
Or
Subman made one that's sumbmerced in his sump using a air stone at its base. Check his build thread

If your using a generic brand of gfo this could be a problem being you stated you change it one every two months. Once saturated it may release back into your water. This is why I use rowa. That say it dows not release once saturated. Also I use to remove any silicates.

As for your prodi bio I dose strontium and iodide seperate with the sea hem bottles at 5 ml every two weeks. I find it cheaper than the prodibio vials

ah, ok :) I'd maybe double the amount for a while and see if that helps.