Help Please

[cweber]

Ive talked to a few members about some problems ive been having with my tank. I know its hard to find a prob without seeing it but i will give as much info as i can. I have a 20g w/10g sump. I have a protein skimmer and cheato in the sump. The tank has been up since March, livestock since June. For the past 2 or 3 months nothing has been real happy. Almost all of my zoas and palys arent opening, i tryed some SPS and all but one monti cap frag has died. A couple shrooms are doin good and my toadstool has its days. I used to do 3-4 gallon water changes with distilled water every week sometimes every other, and top offs were with tap water. I have a lot of cyano right now with tons of bubble algae and some hair algae. I stoped do topoffs with tap water and use RO water for changes and topoff now. That has been 2 or 3 weeks ago. The last two water changes were 5 gallons back to back. My params as of right now are

pH-8.4
Trates-15
phos-0
calcium-480
alk-8
salinity-1.025

Sorry for the large post, i just want some more opinions. I know my ph is a little high but it stays steady, and i could use more cleanup crew. Can the algae be causeing probs?