cory behavior worry

Question
i have a tank with,now, 4 harlequins,6neon tetras,1 coolie loach,3 guppies,2 plecs and 1 peppered cory.
anyway recently i had to change the media in my fluval filter.first time i have done this and i know i should have done it sooner. imagine my surprise when i found one of my coolie loaches in there!i put it straight back and investigated further only to find the skeleton of the other loach stuck in the inlet pipe.
next day we noticed two guppies were missing. i stripped the filter and pipes to no avail.i cant believe i missed two fish, one was bright orange!
tonight i did another 50% water change and cleaned out all the rocks and plastic plants and removed half of the gravel after vacumning it.found part of a body, yuk
to the cory then..eventually. he has been very still and seems to be getting very dark in colour. he also doesn't seem to surface to gulp air and looks decidedly unhappy.i intend another 50% change soon to try and get rid of any nasties thay may have built up.

Answer
Hello,

A 50% water change may or may not help, depending on what sort of nasties you are trying to get rid of. You should check the levels of nitrites and ammonia. This to me sounds like nitrite poisoning, so be especially wary of those. If you prove to have high levels of nitrite or ammonia, then a 50% water change will help and you should do it immediately, followed by a gravel syhphoning and treating your water with a denitrifier, such as Cycle. Monitor the levels closely as they begin to go down.

Also, if possible, check levels of chlorine. If chlorine is your problem, then instead of changing water add a dechlorinator.

I have also had fish who have somehow mysteriously got into the filter. There is not much that can be done. However if you do not have a cover on your inlet hose that has smaller slits/holes in it then you should get one of those.

I hope this helps.

Good-luck,
From Stephanie