Fish not doing so well

Question
My brother has a 10 gallon aquarium e set up about 4 months ago. He had 2 discus fish, 5 neon tetras & a small pleco in it. A discus fish died and then the neons died by the 3rd month. The other discus and the pleco seemed to be doing fine, but he noticed about 10 snails in the aquarium. He didn't know how the snails got in since he didn't add any live plants. About 2 weeks later the discus didn't seem to be doing so well, he was falling to a side, so he did a water change, it revived the fish a bit, but the next day it died, and the following day the pleco was dead. The day after he saw a lot of thin white worms about 1/2 cm long in the aquarium. Can you please advise what could have been going on, and how he can go about establishing a healthy aquarium? Thanks.  

Answer
Dear Durga,
Sounds like water quality is the issue here with the discus loss and the other fish dying. You didn't mention how often the tank was maintained with partial water changes but I think this was your brother tank's problem.

Thin white worms are usually from an excess of nutrients in the tank water from overfeeding or not enough water changes being preformed. They are harmless scavengers but are a sign that there is something wrong with the tank conditions.

Discus must have perfect water conditions. And a 10 gallon is really too small for discus, they would do better in at minimum a 29gallon tank and preferably larger. If you can, test your water for ammonia and nitrites daily until you are certain the tank conditions are stable enough. You can grow young discus out in a 10gal but be sure to move them into larger quarters once they gain some size.

So that's basically it. It's all about the water conditions that you need to see about, especially with such sensitive fish as discus. Test your water regularly and make sure there are ZERO readings of ammonia and nitrite and nitrate is as low as possible. Do plenty of frequent partial water changes, daily water changes are perfect for discus.

Have you cycled your tank also? Cycling means establishing the special good bacteria in your tank which take care of ammonia and nitrite. These bacteria are not present in a new tank and without them if you add a lot of fish the ammonia will rise to dangerous levels. So this is why when cycling a tank, you add only 1-2 small 'cycling' hardy fish such as black skirt tetras or platies. Test the water daily, and preform those vital 50% water changes whenever your ammonia or nitrite goes above safe bounds. The ammonia and nitrite will flucuate in their readings over several weeks but eventually the bacteria will take care of it and get colonized enough to keep it at zero consistantly. But this takes from 4-6 weeks. Patience is vital and don't add anymore fish besides your 'cycling' fish to your tank until the ammonia and nitrite levels are ZERO. Then gradually stock it with a few fish per week and testing your water regularly as well. If you'd like to grow-out some discus in this tank again, first try cardinal tetras or red-nose tetras as your 'test' fish to see how well they do before risking expensive discus. Then if all is well for a week or so with the cardinals or red-nose tetras, either remove them or leave them in the tank and add your discus.
But upgrading to a larger tank should be a high priority if you still plan on keeping discus.

The snails probably hitch-hiked in the bag water when you brought some of your fish home. Just one tiny baby snail can enter unoticed in your aquarium and begin populating it. Snails are not a concern and are helpful scavengers in your tank.

I really hope this helps!
Best of luck,
Karen~