Question
dark red gills 4 fish have died in the last 2 weeks

Answer
Hello Adam! It is very important to check the Nitrite and Ammonia Levels at once. If they are high, a partial water change (1/2 to 1/3 of the water) needs to be done at once and all feeding of the fish should be stopped immediately.
Try adding some PondCare Melafix to help heel the fish.
Measure the Ammonia and Nitrite levels daily and change the water as indicated above until levels return to zero.
(Don't forget to dechlorinate the water when adding the new water). Do not resume feeding until the water quality is back to normal.
Brigitte
www.pondmarket.com