GHA - how to proceed?

[carnthetiges]

15g nano, 8 months old. No detectable nitrates and i don't have a phos test kit.
I've noticed in the last couple of months small tufts of GHA starting to pop up, what looks like red cyano on the sandbed.
I try to tweeze the GHA and siphon the bed but results are short lived.
Water changes approx 20% a fortnight (store bought seawater and topups with RODI).

Bio load is a percula clown, a dottyback and a small flame hawk.
CUC consists of 5 trochus.
Filtration is filter floss and a bag of matrix, otherwise it's just live rock.

I was thinking of adding maybe adding some phosguard try starve the algae, though there's a lot of cautionary threads out there (i've got soft corals and an elegance).
Alternatively would bumping up the CUC (maybe some hermit crabs?) be a better option?
Love to hear peoples thoughts.
Cheers

 

[DrZoidburg]

Zero of anything in closed systems not good. Get that phosphate kit. Try to get the nitrate up. Loosen up on filter maintenance if it isn't clogging. Do less water change, and maybe feed a little more. All are possible solutions. If it doesn't change then maybe a few more snails.