I have an above ground patio pool (30" X 12") with three goldfish. Of late one of the fish is constantly with one of the other fish, almost attached. Whilst I anticipate the reply will be "they may be getting ready to mate", the chaser is half the size of the one being chased. If they have young, are they likely to survive and how many should there be.
A few weeks ago, we treated the water because the fish appeared to have white spot, but that's clear now, and of late i've used greenaway with not much success. ther is no filter, just plants.
It sounds like mating behaviour thats going on and if the eggs are sucsessfuly fertilised you could have hundreds of fry but only a few may survive and make it through to adulthood.
The white spot that you appeared to see could have been breeding tubercals (check Spelling)
What I do to control unwanted weed growth in my gdn pond is wind it around a stick as soon as I see it (little & often) or an old loo brush can handy for the job. All the Best Tbird+