I've had one of those for years now ,couple of other things you could do until it settles start at the highest position on the Cup and gradually work your way down until it stops overflowing also you could turn the tap down until you just got a small amount of air going for it this would deafly slow things up then reset over a length of time until things settle even putting things like bio pellets and also make it go crazy for a few days.
One thing you do I have to check on a regular basis is where the airtube connects to the pump The pump side of it gets blocked with calcium every so many months but this has nothing to do with the way things are going at the moment.
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