If your water is 7.4, it's probably somewhat hard kH wise and a few leaves will barely touch the pH, if at all. It's not like a few leaves will drop it to 5 pH or something. If lucky, you might, I repeat MIGHT get a 0.1 drop. The tannins are barely noticeable, if any.
I don't bother boiling mine, I let them break down in the tank. I rinse them off with some tap water and stick the stem in the substrate. I space them out a few weeks apart, so by the time 1 leave is starting to break down to it's skeleton, I take it out and the one next to it is starting to get soft. I put another one and by the time that one is getting soft, the other one is ready to come out and keep repeating that cycle.
Some people boil them to get the tannins out, but those tannins include humic acids and fluvic acids and other good things for the shrimp, so I rather have those in the tank, and as I said, I don't see a drop in pH because of a few leaves.
20g platy, , 2 x 10g shrimp, 3 x 20g shrimp, 7.5g shrimp and 1 great dane/mastiff puppy.
Sump Pimp #2
My Tanks and my shrimps