More Nitrate Problems & Aquarium Pump Advice Needed

Thanks for the advice. I think more plants is definitely a good idea.

At one point, even with partial water changes every 5 days I was getting nitrate levels of 200!! I've started using RO/DI water and its staying at around a peak of 80 prior to the water change now.

I think I found the original problem as to why my first 2 crabs died. I put a second filter into the water and although it was thoroughly cleaned, I believe there may have been a disease in the previous fish tank (I found this out from the previous owner) and I think it must have contaminated my tank.

Andy