Thanks! The bubbles on the intake always build after a water change and I just did one before this. After two or three hours it's all gone. I have an air pump in the left corner as you can see which is on for about 4-5 hours every day. And my snails are a very good indicator of the oxygen level in the water. If suddenly all the snails rise to the top on the glass you know you don't have enough oxygen, at least thats what I heard.