Last week I decided to make my own CO2 system for my 10gal tank. I used the standard method, 1 cup sugar, 1 teaspoon yeast, 1 teaspoon baking soda, filled with water to 3 inches from top. It worked great, I was getting 3 bubbles every 8 seconds after 2 hours of setup. It got even better after that, 10 bubbles every 2 seconds. That lasted for about 4 days and my plants flourished. Then it really slowed down, 2 bubbles every 20 seconds. Then the yeast, sugar, and baking soda seemed to clump together and sink to the bottom. I shook the 2 liter to get everything mixed up but after an hour it all sunk to the bottom again. Now it is the 7th day and I get 1 bubble every 1m30s. I am using a regular airstone as a diffuser. What could be going wrong?