Question
I bought a 1/2 oak barrel intending to use it as a small garden pond. It was for sale as a planter. It smelled either wine or whiskey. I am a non-drinker. I don't know. I got it water tight, treated the water for five small goldfish, which are fine. I have had them there now about a month, cleaning the water religiously every 5-6 days. I suspect, however, that the bacterial culture which was beneficial to the wine/whiskey, has now started to proliferate on the bottom and the walls of the barrel. I do use a filter, but I need more troops against the molds or the fungus?  The fish seem to do OK. I completely change the water when I clean the barrel, but in 5-6 days it is very slimy again. The slime that forms is white.Could a couple of algae eaters help? Anja

Answer
Properly made alcohol has a complete lack of bacteria.  It is possible that some residue left behind attracted some bacteria later on.  Bacteria will naturally form in water that has fish.  This bacteria is beneficial and necessary to support fish.  You want to only replace half of the water at a time to avoid disrupting these bacteria.

Another possibility is that it is algae; but it seems as if it is bacteria, mold, or fungus.  Fish don't usually eat the latter two but they do enjoy eating bacteria.  There are no hardy algae eaters that don't grow too large for a half barrel.  You could try a small-breed tropical catfish.  You would have to bring them inside for the winter or find them a new home as they can't survive a cold winter outdoors.