I buy a bottle of pure lemon juice at the grocery store, it was at most a buck or two... Note - Not lemonade, but this is just simply pure bottled lemon juice...
I've been using the same bottle for several years now. A little bit will do ya'...
My sister's a diabetic, so I have a good supply of hypodermic needles. I just pour a little bit of the lemon juice into a shot glass, draw the juice up into the hypodermic, stick the needle into the base of whatever I'm trying to do in, and inject away.
For Aptasia, I've found it best to go ahead and pierce the animal, start slowly depressing the plunger while pulling the needle out, that way you're guaranteed some of the lemon juice gets on the inside. It's very difficult to get a needle of anything into an Aptasia without it coming out the other side, so I just make it go out the otherside and use this to my advantage.
Disclaimer - I've never tried this on mushrooms, but if anything will take 'em out and NOT nuke your tank, this is worth a shot...
Other disclaimer - Lemon juice has a very low (Acidic) PH so if you used a LOT of it it could lower the PH of your tank, but you'd hafta use a WHOLE lot of it to do this to a tank of any substantial size. Also, it has sugars in it, so it could cause a bacterial bloom along the lines of vodka dosing, but once again, for the amounts needed to terminate a few miscreants, as long as you don't try to execute a Tony sized Xenia colony all at once, it should be fine...
