Hello and thank you for your inquiry. I'm sorry to hear about the issues you are having. The first thing I would suggest is going with a larger sump. A 10 gallon tank is simply too small for that size aquarium and in the event of another power outage the same thing could happen again. I would recommend going with as large of a sump as you can fit under the tank, ideally something at least 24 to 30 inches long and 18 inches high.
As for your aquariums water chemistry, it sounds like when you had the die off it did cause some cycling in the tank and more than likely you still have some build up inside the tank (possibly trapped in the rock and/or sand). I would suggest starting off doing some good sized water changes. Doing weekly 40-60% water changes and siphoning out between the rocks during the water change. I would recommend doing this for at least one month, if not two. This should help to bring the water chemistry back to where you want it and then from there doing monthly water changes and the use of additives/supplements or using a calcium reactor should help to keep them stable for you.
If there is anything else we can do for you please let us know.
Marine Depot Customer Service