Actually, if you want to switch to chlorine, you may NEED to drain the pool. The problem is, chlorine will convert the used up bromine in your pool, back from bromide into bromine again.

In fact, if you look closely at your bromine containers, you'll probably see a chemical name like bromo-chloro-dimethyl-hydantoin. They can make 2-bromo-dimethyl-hydantoin, but the bromo-chloro version is cheaper, and once you've got a little leftover bromide in the pool, all of the active sanitizer in the pool is bromine, regardless.

Another version of that info is this PoolSolutions page that I wrote 15 years ago.

Is your pump a 2-speed pump? If it is, that will help.

Can you do the DE-test? You have to be able to see the point where water emerges from your pool return, in order to do the test. => http://pool9.net/de-test. Doing this test will allow you to determine whether your filter is working adequately or not.