Fish Dying

[Comacchio]

Well after cycling my tank for almost 8 weeks, my tank finally nuked 5ppm of ammonia into nitrate in 12 hours consistantly for 7 days. I performed a 100% water change and redose with 5ppm ammonia on the day before fish day. I tested the tank 12 hours after dosing and again it had eaten the ammonia. I then went to the fish shop and bought 2 keyhole cichlids, 2 bristlenose plecs, 10 harlequin rasbora, 8 neon tetra, 6 panda cories and 3 platys.

Everything was acclimitised over the space of an hour then added to the tank. All was fine for 3 days when I lost my first harlequin. This is where it started to go wrong.

Now a week after adding fish ive lost: 4 neons, 3 harlequins, 1 panda cory and 1 platy.

I've been checking levels twice a day - 0 ammonia, 0 nitrite, ph around 6.5-7 and nitrate under 100ppm (Been doing PWC to bring this down to nearer 40 (Cant do large water changes when my tap spits out water at pH 5!) and I've ordered lots of live plants on ebay ready to come through this week)

What the hell is wrong?!

 

[Dieses Madchen]

You can do a large water change and buffer with bicarbornate. This will bring the pH up. i use baking soda when need be. It is harmless to the fish. You can also add some limestone rock decorations to raise it.
http/freshaquarium.about.com/cs/waterchemsitry/a/mathcph.htm

How do you introduce your fish to the tank? Next time you buy fish, check the parameters of the water in the bag with the fish and see how well it matched your tank water. You made need to slowly mix the tank water in with the fish store water (in the bag, not the tank) to slowly acclimatise the fish to your water.
http/www.liveaquaria.com/general/general.cfm?general_pagesid=19