HELP, Shrinking sea mat ??????????????????

Hi,
I got a sea mat frag 2 months ago . When I bought it it was green and
nice sized polyps. now the polyps look like they are smaller than when I got them. Whats going on. My colt also died over a 4 week period?

tank specs
20gal Long 6 mo old
15 gal sump w/trickle filter bio balls
2 power heads gph? plenty of flow
10 lbs of LR
Bare bottom / for now
5 gal refuge w/ ? sea weed algea ? forgot its not any of the usual algeas
that is also BB/ for now thinking of DSB.

2 maroon clowns juv
1 coral banded shrimp
1 anemonea pink tip condy doing great doubled in size. its the first thing I got.
2-5 hermits some died, I know I have at least 2
1 turbo snail

I had some high nitrates 60+ppm
I got It down to 20 I'm going to try for lower. I didn't want to do too many water changes too soon. I got rid of the RED slim algea witch was
a problem for a wile. I got red slime remover.
My green algea is very little.

ph 8.0 - 8.2
nitrates 20
nitrites 0
ammo 0
phosphates 0-0.1 test kit sucks It should be low
cal 450
iodide ???? no test yet
mag ???? no test yet
kh 300 I think going off of memory
stro ???? no test yet

Other than nitrates my other chems have been the same.
Should I be testing for Iodide , Mag , Stron .
I do add supliments rarely. I figured that my salt would have enough for what I have in the tank and the amount of water changes I do.
I can't figure out what is going on with my corals.
I am trying to take pics to show problems to get better advice
Thanks
everyone !
Howie

 

Its the size Like they are getting younger

 

You might be right ! The LFS I got the polyps from had them under
2 actenic ho or vho not sure but my tank is brighter for sure.
Oh yeh I have a 65w PC 50/50 and 2-24w T5s actenic.

My colt was doing great It was a frag it grew like 1/3 bigger grew new stalks and ond day started to get smaller and close up till I was cleaning
the tank blowing crap off the bottom with my power head and it blew
the colt right off the piece of live rock I had grown it to. well I noticed
that the underside that was attached to the LR was gone. like something
had dug in it. I did see a white worm thing in one of my rocks the other
night after I turned off the lights. Then the next day there was a little
maggotty looking thing on the bottom. It could have been him not sure
if it shriveled up or if it was another one.
any ideas'

Thanks again Howie

 

I don't think you have enough light. Sometimes the appearance of brightness can give you a false impression of the amount of light there is. If your LFS had HO or VHO lights on their tank there is no way that a 64w pc could have a superior par value. I would guess that you have plenty of actinic lighting with the t5s but one 64w 50/50 pc may not be providing enough full spectrum light. I have a 20long also and I currently have a 96w pc 12000K full daylight for white light. The tank looks very bright but I know that I really am only running med light levels.

As for zoas, sometimes they get taller etc...under low light like missionsix says. I have also witnessed them shrink away to nothing under low light. Like SPS corals, zoas can have a variety of light requirements--anything from very strong to low levels, depending on the species.