I got a 200 gallon stainless tank with insulation on all sides and bottom. Got a pond filter in take with roughly a 600 gph flow. I have filter media around intake of pump and pump feeds into a 5 gallon bucket of bioballs. Needless to say minnows have been dieing to quick. Losing 1-2 dozen a day. Tank had been up for maybe 2 months minnows in maybe 3-4 weeks now. I've been changing 100 gallons of water every 2-4 days and feeding them every 3-4 days. I had 2lbs to start which ik is a lot for new tank but expected the lose of them so wanted more to start. Water temp round 64-70 degrees and using rain water from my neighbors cistern. I've been testing ammonia and it's off the charts even after the water changes. I don't know what to do. I'm about ready to give up but my local bait shop has been out 3 different times this year. Any suggestions.