~30 gal pond: dying floating plnts, fish, other plants OK

Question
I have 3 questions, all related. Q#1: I have a large, antique washbin approx. 30 gallons, that I'm using for a water-garden. It is galvanized, but appears to have sprouted a couple of rust spots this year. For some reason this year my water garden has been plagued by a red-brown slime which coats just about everything under the water level, but does not cloud the water unless disturbed. What is this slime, and how should I get rid of it? Q#2&3: I have 4 chinese mountain minnows that are healthy; I rarely feed them- they seem to be feeding on the mosquito larva they find, as well as other things I'm guessing. I also have  very healthy juncus, spider lilly, and cyprus in the water garden. The problem is that after a couple of weeks all water lettuce I introduce turns yellow and the leaves begin rotting off. Water hyacinth also tend to get brown spots then blacken, finally rotting and dying. Twice this year I've started with new water lettuce & hyacinth with the same results. Even the duckweed tends to die off! My question is: are these rust spots (2 nickel sized spots) causing this dying off of my floating plants? Is it also responsible for the red-brown slime that coats everything in the pond, including the sides of pond, submerged plant containers, and some plant foliage? I appreciate any help you could give - I've tried barley grass w/out ant luck. I really miss the beauty of the floaters, and the fish like the cover they provide. Thank you much, Lisa

Answer
Hi Lisa,
Thanx for your question  Without a doubt, galavinized containers contain toxic metals such as lead that are harmful to fish with prolonged exposure.  The rust spots also contribute lethal dosages of iron to the water that interact adversely with the fish's gills, causing death.  I believe the rust spots are also contributing to the red-brown slime.  All of this is contributing to an unhealthy and toxic environment for your fish and plants.  I would use something different like a whiskey barrel half with a pond liner.  I hope this helps.
Tom