Zoa/Paly Help

[troutbum24]

I cant seem to keep zoas or palys alive any more.
When I first got my tank (used) it hadnt been taken care of and was quite dirty. I had great success with my zoos and palys until eventually they all except for a tiny portion of one colony all melted away.
Unsure of why this all happened I decided to swap out my sand bed for some new fresh sand thinking maybe i was leaching phosphates. So last June I swapped out sand bed and everything has seemed fine (BTA's, monti, frog spawn, and acro's doing good, my red planet finally started growing that I got over a year ago that went from red to green and is now red again.)
I have a pretty good clean up crew in my opinion about 10-15 hermits, 1 emerald, and about 10 snails. I have been religious with water changes last two months changing 5 gallons a week from 53 gallon total water volume system. Keeping all my parameters in check
Temp: 77.5
Salinity 1.025
Ph: 8
dkh: 9.3
Mg: 1300
Ca: 480
PO4: < .25
Running Apollo LED's all zoo's paly's are in lower portion of tank and some are partially shaded.

However I recently put in some zoo's and some montis. They lose color within 1.5 weeks and ever so slowly i notice fewer and fewer heads left. A friend suggested dosing iodine? I went to LFS and asked and he said if im changing water weekly i shouldnt have to dose Iodine, but recommended a iodine dip (Seachem coral dip) anyhow I did that last night, no nudi's, astrea's or mites came off.
I've been reading that having a clean tank might be an issue? any way to dirty it up? aquavitro coral fuel maybe?

 

[fity2pounder]

I have also heard that too clean of a tank can cause zoa problems. I have to disagree though. I currently run a tank with no sand bed and no live rock (except in sump) at all and the tank is basically spotless. My zoas are flourishing. I don't do water changes very often though. From my experience, I think you are doing water changes a lot more often than necessary. Perhaps try doing water changes only like half or a quarter as often as you are and see if it helps maybe? Or maybe try doing a 10 gallon change once per month. Sometimes doing water changes too often will mean that your watch chemistry is constantly changing which is never good for any zoas in my experience.