Nitrates are 0, I just have a fluval 205 running like i have for the past 2 years and I was just gunna install the skimmer and the powerheads, all this happened in one night after i installed the 2 powerheads. I clean the filter alot so it cant the putting nitrates in there.

Well, your salinity is too low. :p

Can you post the link you found with this similar problem? Any tips from that thread?

The fish in that thread had a major ich attack, so maybe they were stressed out by the change in the flow in the aquarium and they got ich. Ich will attack the gills of the fish first so before there is even white spots on the fish their gills are covered with parasites, thus the heavy breathing.

I do not beleive that the problem in that thread was caused by the new pump, rather it was caused by the ich attacking the gills of the fish.

Probably the person putting a new pump stressed the fish out while doing a more extensive maintenance and work in the aquarium than usual, and since that person had ich present in the aquarium, it simply took the opportunity and spead on the fish.

I put 2 koralia evolution 1050 in my aquarium and never even washed them. No sign of any problem with my fish...but my fish don't have ich so they don't get sick at the slightest stress.

well ive never had ich in here before, man im so confused:sad:, it could be anything at this point i just hope the damage has been done and i can ride it out.

I'd put money on you having an issue with a protein film on top of the tank. This prevents oxygen exchange and tends to happen in mature systems running a cannister filter (205) and no skimmer ( or a cruddy skimmer)

It's not the powerheads.

Take both powerheads and point them at the surface of the water, from About 3 inches under the surface to agitate the waters surface and break surface tension .

3 hours later, when normal oxygen levels are reached and maintained, fish will act normal

+ 1 on that. No skimmer and a greasy fil at the surface is probably pushing it. At first I was shutting down my skimmer at night because I thought it would help my fish to sleep better because it is a bit noisy in the water when the skimmer is running, but after seing my fish breath very fast in the morning I resumed running the skimmer 24/7. I have not seen my fish do that since then.

im just wondering why they all started breathing heavy when I introduced the powerheads, thats why i am hesitant to put them back in.

It could be an unfortunate coincidence. The fish death may have happened even if you had not added the powerheads. If death by powerheads was a common thing there would be a lot more threads and discussions about it. I've searched and can't find anything (other than the thread you linked) about death by powerhead. Well, aside from the usual fish swimming into powerheads and getting chopped up.

Film on the surface of the water is definitely not a good thing though.