My fish get worms all the time too - it's their favorite snack! When I'm working in the gardens near the pond they all hang out near the edge just waiting for me to toss some in.
I'd leave the pond bottom alone for now - like I said, it may or may not be causing issues. My most likely guess would be it's feeding the algae that you're experiencing as it's loaded with nutrients.
The floating islands are fun and pretty, but unless the roots are able to get in the water, they aren't really doing much for the pond. More plants in the pond itself would be more beneficial and especially if they are planted directly in the pond - no pot. They will love your pond and your pond will love them! Can you plant things in the top of your biofilter? That's a great place to get more plants in the pond. Some people put floaters in the top or a nice taro plant. Both will help with filtration and make your biofilter prettier! You can do floating islands as well, but like I said the roots need to be able to get in the water.
Focus on the big picture - more filtration, more aeration, more plants - and your pond will slowly balance out. I know the green water is frustrating and you probably won't believe this part - but get things moving in the right direction and it will clear so fast your eyes will pop out of your head. Like overnight fast. Like Jimmy John's fast - haha !We've seen it happen here on the GPF time and time again. Patience pays off. The long term solution is the best approach - far better than constantly having to treat the pond and risk doing more harm than good.
Post some pictures of your pond - we love pictures!