First, warm welcome to AQ.
From your description (apart from the colour) the snails in your tank appear to be Malayan Trumpet Snails (do a search, or post a photo). If it is... you can be sure it is not the snail that is causing the problem. The MTS is an algae and detritis eater that comes out only when the lights go off. They will help you keep your tank free of algae.
They do, however, reproduce very prolifically, and the yoyos will generally not eat them. Even puffers will only eat the very young ones.
I notice that you are running an airpump. That could be one of the problems as the agitation resulting from the air-bubbles may result in CO2 lost. Beyond that you will need to specify more accurately your lighting duration and fertilisation regime, etc for some of the experts resident here to help you.
/John
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