Never heard of mosquito fish but your container is not big enough for fish to survive in especially with 3 al those plants. In addition what is the metal? Some give off toxins that will kill the fish. Reality is you have a nice container for growing plants in but remember it needs drainage holes unless they are aquatic plants.

Really like your picture, your garden looks lovely any chance of seeing a few more pictures?

the metal looks to me like galvanised tin which i think is only toxic if it is burnt ie welded etc etc unless it is aliminium that would account for a film on top but again only if heated as boiled.if in doubt get rid and buy fibreglass or plastic.good luck.

Mosquito fish are little fish used to keep small bodies of water from getting infested with mosquito larvae. Unfortunately, I believe that they find galvanized metal toxic, so you might want to try feeder goldfish, instead. If they die off, you will need an aerating pump, or a small submersible circulation pump.

tugbreath is right on the money . lots of heavy metal isdeadly to fish . strangley enough lead is fine as it gets an oxygenated layer over it to stop its normaly very toxic seeping into the pond . dont do it in a marine tank thow as the salt stops this hapning . the best thing you can do is bury your tub and put a good quality pond liner in it . put some nice stones hanging over the edge and in a year it will look natural .

The tub from old farm may had some traces of oil or fuel to give an oil film on the water??

egsactly jiffy x .

Let's look at the fact those plants are stood on stones in pots in soil... not good in any pond situation.

i dont know what you mean moon sorry x .

The plant in the upper left quarter (Sagittaria?) is planted in soil and/or stones, but the rest are floaters--water hyacinth and water lettuce, to be specific. If the potted one has too much organic matter in the mix, that might account for the dead fish and greasy film, too. About what part of the country are you in, Sylly? Hot weather will compound the problems of lack of circulation and too much organic matter.

i agree tugbrethil . water thats cold with know salt and protien in it has the most oxygen . the hotter and or saltier it gets the less water it has the capassity to hold .