2 dead chromis and dying stars.

[teza_125]

i am running a 25 gal saltwater aquarium. mostly live rock with 2 small hermits and 4 green chromis. the filter is under the tank, plain square kinda thing with inlet and outlet for the water (i know thats obvious) and 3 basket layers with different stuff in them. we started with 2 chromis and everything was going super. waited a month and added 2 new ones and everythings been going well for over 2 weeks (all eating and acting happily) until 2 days ago we had a leak in the tank and had to re seal it and so did about a 3/4 water change. the heater also broke so we had to wait overnight to get a new one. yesterday one chromis died and the other was hanging above its body breathing fast and not moving much (we dont have a qt tank). also our large blue star it lying on the sand looking really weak and about to die and our brittle star is having trouble moving also (i have just been informer the brittle star might be dead now). we got water checked today and
ammonia 0.25
nitrite and nitrate both 0
ph 7.8
phosphate 0.75
salinity 1.028
tried to get salinity down earlier after test and now second chromis has died (not sure if they are the forst pair, second pair or one from the first and second lot we got)
any ideas what could be killing everything in the tank?

[sqrle]

What about the sealer that you used? Did you give it 24hours to dry before putting the fish in the tank?? Did the water ever come in contact with the wet sealer? This stuff is toxic when not completely cured and dry. Your salinity is way too high as well. If you fluctuate your salinity levels too quickly you will shock and potentialy kill the fish. You also need to get your Ammonia down. All of those things could have played a part. Not to mention the broken heater. How far down did the temp. in the tank get to, and for how long?

[teza_125]

heater was down overnight about 10 hours i think but that was a few days ago. the sealer was one you can apply while the tank is still full (it was half empty tho) and was suposedly non toxic. lowest the tank got was 22 degrees C