This might be a silly question? But why do you want to remove the sight glass?
I took a quick look at my intex 16” sand filter and as near as I can tell the sight glass is just screwed in. I didn’t actually try to remove mine, because, well, I want it to remain where it is. But if yours is anything like mine I believe that you should just be able to unscrew it.
I wouldn’t worry about algae inside the sight glass too much because water only goes through the sight glass when you are backwashing or sending water to waste... and any water the passes through the sight glass is not put back into the pool.
It just screws off. Use a cloth wrapped around it so it doesn't scratch, and some channel lock pliers. But, that water goes out, not in. It does make it hard to see if the water is clear, though, when you backwash.