This overly-stuffed DROP1.2 or 1.2x needed a good cleaning/brushing a while ago. Not only does the growth block water and bubble flow (which is why the growth is bright yellow, because it can't get iron and nutrients), but it can block the circulation holes in the case so outside water can't get in. So a good brushing (including the door, on the left) in a kitchen sink will fix it. Take that growth, and fertilize your garden with it.
Note also, the top of the yellow which makes a line across the top of the case. This is the waterline on the inside; if the top air hole gets blocked by growth, this waterline will drop lower and lower as the inside fills with air (because the air can't get out).