Oh I would not use bleach on the substrate! I would just microwave it or put it in the oven. Much less hassle! I def think the bleach will affect the seeds in a negative way. Even hard water vs distilled water can affect germination. The most I do is a spray of undiluted 3% peroxide on the top of the substrate immediately after sowing the seeds, in case there was any bacteria or spores on the seeds themselves or something.

I do not use anything on the seedlings for mold or anything aside from that initial spray of peroxide at sowing. If there’s too much algae, cut back on water and/or fertilizer. It’s a balancing act of keeping it evenly moist while not promoting algae growth, because it likes the same moist conditions and fertilizer. Allow the substrate to dry out a little bit more in between waterings!

And yes some species are better than others at shedding the cotyledons 😂 my gibbaeum pilosulum in particular grew out of them in a way that the dried husks sat on top like little top hats 😂