I agree completely about minnows dying during water change cycles. I believe that this is due to temperature difference, not the water change itself. Minnows are very temperature sensitive. As little as 4 degrees difference will shock the little rascals and cause them to give up the ghost. Filter will help a lot by keeping the same water. The 5 gallon bucket filter in my pic has been filtering the same water for over 2 months and keeps the water crystal clear. When I do change the water I temper them. I pull the water level down a few inches the start the water into the tank to get the temp equalized. Then I can open the drain and take about 2 inches off the bottom . Close valve and fill it up.