Autumn is a bad time to introcude fish to a new pond really since they dont have enough time to settle in before the water coos off.
First thing is to check for all the normal parameters. You want 0 nitrite & Ammonia, 0-10ppm Nitrate, plenty of O2 and nice clean conditions. You want a PH of 7.2-7.5 for ideal purposes or up to 9 in water with a high calcium content, i.e hard water.
Algae is not necessarily a problem other than the fact that you cannot see the fish. Other things to check include making sure you either condition your tap water or use a decent de-chlorinator. It may be a good idea to check for copper in the water just in case.
Don't be tempted to perform a large water change incidently unless you have good reason to suspect a toxin has entered the water column. Even then , I would place large bags of Active charcoal in the filters rather than resortt to a large water change. You need to be aiming for around a 10-20% change per week in normal circumstances.
You must identify the nature of the problem to rectify it of course so once you have elliminated water quality as an issue, I would advise you to net one or two fish and have a good look over them. If you cannot see anything obvious you or an experienced freind need to perform a skin scrape and look for parrasites. These things can be quite prevelant during early spring when water temperatures slowly climb as they are beginning to now. Parrasites can take advantage of weakened fish very quickly indeed so it is vital to rule them out or indentify them and treat the fish & pond accordingly.
Alan F.
Posted on Apr 8, 2006, 12:08 PM from IP address 213.120.101.21