For the snot problem I would be flushing. And flushing some more. I would flush with a fungicide like the one I linked. I think Serinade is a more popular fungicide, not sure. I would do a combination of following directions and using your judgment, but in general I would drain the res and fill it with some solution of water and the antifungal. Start at a low strength to make sure it doesn't have an adverse affect on the plants. Turn on the bubbles and anything else that helps circulate, and let it sit for an hour. Dump that and start again with a slightly stronger solution, and keep doing it until you reach recommended full strength, or beyond if you feel adventurous. I would think after a day of this treatment the snot should be mostly or completely gone. Just my guess though.