I'm sure more details will be asked but this starts to help. If by topsy turvy you mean in a vertical sort of way - my clowns do that at night for hours. Until about a week ago, then they both found a rock hole they now 'sleep' in. It's pretty neat. But that's a side note. Your Nitrate reading is pretty high. I bet if you test for it, your phosphate reading will be high too. Most likely due to overfeeding. Crabs will find enough to eat, don't worry about them. They're point is to clean waste of sorts, not to be fed, ya dig? Your salinity is very important to know too. If it's too high or too low it can easily kill fishies. Or if it's inconsistent. Is that Ammonia reading a spike and has been 0 for several weeks or has it kind of hovered up there? If it's hovering, you're probably adding things before the cycle is done and keep kicking off mini-cycles. I say this because you've lost several fish in a row now, while still not too old of a tank. Your schedule of filter/water changes sounds good with one caveat. You shouldn't even start to count those weeks until after your cycle. If you have been, it may be another reason your cycle won't finish. I'm sure others will respond too. Go ahead and post some pics!