11-06-2008, 01:07 AM
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I can't address the illness as those symptoms aren't something I'm familiar with. However, before administering any sort of medication, I would absolutely work on improving your water quality. 40-80ppm of nitrate is very high. You should do water changes on a regular basis to keep it under 20 ppm if at all possible.
Sorry to be the bearer of bad news, but the fish you have aren't going to work out in the long term. The goldfish you have is a coldwater fish and thus needs to be in an unheated tank in order to thrive. The bala sharks, on the other hand, need tropical temperatures. Whether your tank is heated or not, some of your fish are suffering. If your goldfish is a fancy variety, a 30g tank is suitable for one goldfish for long-term care (although the bigger, the better). If it's a regular comet goldfish, it will grow very large and thus needs a much larger tank (75g would be good, 90g would be great). The bala sharks also need to be in a school of at least six and, as they grow to over a foot in length and are active swimmers, really need to be in a huge tank. You won't be able to keep them in a 30g tank for very long.
A school of tiger barbs and a single rainbow or red tailed shark would be much more appropriate for a 30g tank.