Vacuum to waste?

Hi All,
I have a question about vacuuming to waste as I have never done this before.
I'm currently fighting a little green algea and have gotten my results back in line and am hitting the pool hard with chlorine. I was wondering....do I have to vacuum to waste or can I just vacuum and backwash? I only have a 18' AG pool so I'm afraid if I vacuum to waste I will be losing a lot of water and have to refill. Is that how vacuuming to waste works?

Thanks in advance for any help.
I have learned more here in a few weeks than I have in three years of owning my pool. You guys are so helpful.

Thanks again.
Joe

Sometimes it gets so bad you have to backwash every few minutes. If that happens, you might as well vac to waste. Also, some filters won't catch the algae and will blow it back in the pool. If you can live with your backwashing frequency and the pool is getting clean, then do it that way.