It doesn't take much PO4
to promote cyano
growth. If you are detecting some with a test kit, that is probably enough. I bought a PO4
reactor from www.marinedepot.com
and it cleared mine right up. Two Little Fishies makes one but they are kind of hard to find right now. I bought the new one that Kent Marine makes... works very well. I think I paid around $35 for it. You'll also need some 1/2" inner diameter tubing, Phos-ban or Rowa-phos, and a power head that pumps 80-90 gph
thru it. I hooked mine up in series with my UV
sterilizer so I only need one powerhead to run them both.