Oil layEr

There is a layer of oil on my tank’s water surface that seems to have caused the death of my Arowana and sucker-fish as well as made the rest of my fish sick. I suspect the oil comes from the new water hose that I’ve just bought. How can I find out whether it is the cause of the problem? Besides scooping away the water at the surface to remove the oil, is there another method or a chemical that can be used to solve this problem?

Personally, I have never encountered this type of problem before. To the best of my knowledge, a hose is usually sold clean of any solvents. Whether new or old, a hose should not leak out oil-based solvents.

There is a quick way to find out if your new hose is the cause of your problem. Fill a small pail with water using the hose and put the pail in a brightly-lit place where you can see sunlight hitting the water surface. The presence of oil will be marked by a patch of thin film on the water surface that reflects rainbow hues, or a film with a whitish to yellowish tinge. If that is the case then, somehow, traces of oil are present in your new hose.
Getting Rid of the Oil Layer In the Fish Tank

Getting rid of the oil layer is a tricky business. I do no advocate the use of chemicals to dissolve it. Neither would a surface skimmer solve your problem. This might remove the film of oil from view but some oil would still remain in your tank’s ecosystem. Instead, try this method:

1. Take a piece of newspaper. Cut it to fit three quarters of your tank’s water surface.
2. If you are using powerheads and filtration systems, cut off the power supply and wait for about 20 seconds for the water current to stop.
3. Slowly place the newspaper flat on the water surface. This is the part where experience helps. Do not despair if part of the newspaper gets submerged below the water.
4. Stand at one end of the tank’s width. Hold each corner of the side of the newspaper nearest to you, and slowly pull the newspaper up and towards you. As you pull it up slowly, the newspaper will pull the film of oil together with it as it breaks contact with the water surface. You may have to repeat this procedure a few times before the oil film is completely removed.