We have a 55ga saltwater tank that has been going for almost 3 years. As of right now we only have a clown and a chromis in the tank with the addition of a few hermit crabs. We had 2 fire shrimp for a little over a year and all of a sudden they died. I do routine water changes, but after the shrimp died I tested the water and everything was normal except the nitrate levels were crazy high. I have done numerous water changes (weekly) since then and it was still high. I spoke with our local saltwater store and they recommended doing a 50% water change. We have an over the tank filtration system (I know it's not ideal).. We are looking into getting either a canister filter or sump.. But for now they gave us some other filtration to put behind our normal filters that is supposed to help reduce the nitrate levels quickly. It has now been a week since doing that and I tested the water again this morning and the nitrate levels are still high. We only feed our 2 fish once per day, and honestly only a small pinch of food. I was wondering if anyone has any advice for what we should do. We would love to expand our tank and add more fish, but can't with these levels. Would adding more live rock to what we already have help with the nitrate levels?