All the fish in my tank are dying, why?

I have a 60 gallon saltwater tank that I set up about 3 months ago. I started off with Damsels, and gradually added other species until I had an nice colorful mix once the tank was well established and had cycled properly. We lost 2 damsels and a tomato clown in 2 weeks, then things went well for about 3 weeks. Everybody was happy and friendly, including the damsels (3 small) tomato clowns (2 small), horseshoe crabs (3) small dog-face puffer, yellow tang, fire fish (2) and one peppermint shrimp. Now they are dying at an alarming rate. We did get a reddish colored algae of some sort showing up on the glass, and I treated for it. The instructions said to remove my carbon filters and turn off my protein skimmer, so I did. Even with the treatment and limiting filtration, i am still losing fish. The only thing that is different as far as I can figure out is that I bought my saltwater from the fish store rather than making my own using instant ocean. We are running a 350 and 200 bio-wheels (carbon filters changed every 2 weeks), and a good quality protein skimmer. Any guesses or suggestions? I have tested and the ammonia, nitrate, nitrite, and ph are all reading really excellent (the best readings I have gotten since I set up the tanks with colors exactly matching the comparison cards). Please help? I only have my puffer, 2 damsels, 2 horseshoe crabs and my peppermint shrimp left and they are starting to look poorly!All the fish in my tank are dying, why?
How often do you perform water changes? What's your temp at? I'd perform a 30%-50% water change immediately. Are you sure to wash your carbon filters after every change? Was your tank cycled?

EDIT!

-At once every two weeks, you're changing your filter cartridges a *bit* early, but I doubt that's the problem here (unless you are cleaning so well the biological bacteria are being killed on any decor, in the gravel, and on the filter media). What are your water parameters (nitrate, ammonia, nitrite)? Airation may be an issue here, though I can't be positive. Make sure that when you are cleaning any part of your tank (except the glass outside!) to never use regular, untreated tap water or any sort of cleaner.
They might not be liking the sudden change of water (from instant ocean to ready-bought)



Big big big nono :) Option? If you ahvent already tried, I would try throwing back in 50% instant ocean one day, and again the next day, and again the next day.



Make sure you use a siphoning technique to get water in and out to avoid stressing the fish out.All the fish in my tank are dying, why?
some fish may not need to be in saltwater and maybe your not feeding your fish properly. you don't need to change the filters a lot. once per 3 months would do. u may also need those long tubes you put into the water. my fish die a lot too but after i put the long tube you put into the water my fish didn't die anymore.
1. I can't tell if you're saying the tank has had fish the whole 3 months, or just about 5 weeks, either way, this is a salt water tank, and rules that are easy to break with freshwater, are not going to be as easy to get away with now.
2. tank will eventually be too small for the puffer
3. red algae is actually a bacteria, and means you have or had too much waste, the treatment sometimes can screw up your biologic filtration. And turning off the protein skimmer only makes matters worse. Yea, I know that's how the treatment goes. But reducing the waste would have been the first thing to do.
4. shouldn't even need carbon all the time and if there's any ammonia removing filter material (white rocks) stop using it. I never ever use the ammonia removing filter materials, they all cause problems.
5. and turn your skimmer back on.
6. do a small water change, and pay attention to the salinity and your choice of water conditioners, it's the one thing you didn't mention. I use Kordon brand, Amquel and Novaqua. Don't use Ammolock.
7. unless this is a reef tank, don't get shrimp or other crustaceans, I'm still surprised you even have a shrimp, perhaps you're overfeeding so much that the puffer hasn't noticed him yet. But a puffer will eat the shrimp first, and eventually start chewing legs off the horshoes.
8. yea that too, are you overfeeding? I thought so.
9. 60 gallon with regular petstore filters is not going to be easy, the tank is small, and even bio wheels are not always up to handling a salt water tank, especially without regular water changes.
10. So, rethink what you expect out of this tank, and find a more realistic bunch of fish and think less fish and less food, especially until you have some better success, then you might have a chance.

edit, I re-read your question, and you had fire fish too? yea, ok, you really need to slow down there and get really hardy fish only. You've already tried at least 3 or 4 completely wrong fish for a 60 gallon and a couple that only routinely live in the healthiest of reef tanks. Either you weren't listening to the fish guy/gal at the store, or they were idiots. Try again when the tank settles down.All the fish in my tank are dying, why?
Peetr is on the right track.



The tank is still new, barely cycled and you are stuffing all sorts of random fish in there.



The red algae is a sign of things in the tank not being in "balance", excess nutrients are feeding the bloom of algae or bacteria. Sure you can add chemicals to kill that off, but that is only treating the symptoms, not the underlying cause of the problem. The chemical treatment and lack of the protein skimmer then make the water quality even worse.



No more fish, work on getting the tank stable and stocked properly, do some extra water changes etc. It's not a competition to see how many fish you can stuff in the tank



Ian
Dont wash ur tank with soap