Very true..it would be hard to get a pic, however, hydra generally are not harmful to adult Betta-they can kill fry and even give you a tiny sting-doesn't hurt too bad but it can startle you a bit...at least it does me.....
I'm not sure about the white algae, if you can post a pic I'm sure someone will know what it is. I have been seeing in my tank what looks like a clear piece of thin film with little dots or eggs on it. I assume it's snail eggs since it started after I got snails. Also, another advantage of snails is that they are sensitive to water conditions. When your water needs to be changed they will all go to the top of the tank to get either oxygen or to get out of the water, and they do this before the water starts to affect your fish.This morning I had about 75-100 snails at the top( I had no idea there were this many). I tested and nitrates had gotten high. I did a water change and within 15 mins they were back to the bottom.