I hope someone can helkp. I'm stresses over this.

3 weeks ago i added 12 cardinals to my discus tank. By the next night 11 were dead. The following night the other one was missing. I got 9 bodies out of the 12 out of the tank.

2 Days later i noticed that a breeding pair of splendid betas were missing.

Next day was my normal waterchange day. I have a 6x2x2 heavily planted tank with 9 discus. 12 cory's, 2 albino bristles, 4 loaches. 12 ottos, 6 flying foxes. I usually do a 30 percent change every 4 days. I use aged water always (4 days cycling). I could not find any bodies during the change but with lots of wood and plants and i run the tank at 28degs i assumed they dissolved.

I also run UV and denitrator. I dont use co2.

I use 3 filters - ehein 2217 on the uv. 2213 with phosphate remover in it also. And a 2028proII with the denitrator. I use siparex (spelling) in all filters.

My normal water condition is. Ph6.8, 0 Amonia, 0 Nitrite. Nitrates are usually inbetween the yellow and the next colour but low anyway. Phospate is 0.

A week later i bought 3 new discus. 2 small b.diamonds and a medium cobalt. Had them in a small q.tank for a week then put them into the main tank. As i was adding the new fish i noticed a couple of my other discus not the news ones were flicking on the plants. Sometimes they do that for show but as i was adding the new fish i was thinking... i hope there aint no fluke infestastion happening.

The next day it was obvious that there was a problem. All of my fish were flicking but not the new ones. I decided to do a course of sterazin immediately. But did a water change first. And turned off the UV. By the second dose (day 3) the new fish were flicking also. And the new blue diamonds were dark.

Everyone is eating though except one blue diamond who keeps hiding.

I completed the 1, 3, 6, 8, 10 day dose as per the bottle but still the flicking was happening - didn't seem to be any better at all. Also very evidend scale loss from the scraping was evidend from flicking on the wood. Some of the discus also seem to tilt sideways and let the other ones pick at their bodies. I presume that this is something they do - or maybe not. they then start swimming again normally.

The flicking seems to happen mostly just before lights out when there is a lot of fin quivering and darting and flicking on tlants and wood.

Because of the scale loss i decided to dose them with promethusyl. Did that the day after the last serazin dosse but did a water change first.

That was 2 days ago and not i am at my whits end as nothing seems to have improved.

I dont know if the cardinals added some nasty bug into the tank that took 2 weeks to run down the dicsus to the poiont that parasites took over but that is what i am thinking. Dont think the new discus brought the problem in as it happened to them 2 days after.

I though that after the cardinals dies that the uv would handle whatever got them. Also the uv has a brand new tube and is working fine.

Anyway this had become a little long but i do not want to follow the advise of the aquarium i got my cardinals from (and all of my other fish) as i did find out that the cardinals were treated 4 days b4 i bought them for some fungal infection but they didn't tell me and they looked fine. I am not going to buy any more fish from them.

Any advise would be appreciated.

Also the only visible signs on the duscis is the damage from scraping plus a few little pimple like bumps - whitish on a couple of them.