I'm probably being laughed at for even asking this question, but I was just curious. When the time comes to change our spa water, is it a bad idea to drain it into our chlorine (BBB) pool? Will the left over bromine eat up my pools chlorine?

Don't do it. Once you put bromine in the pool you have a bromine pool, which is somewhat more expensive to maintain. The only way to go back to a chlorine pool is to replace 100% of the water.

Ok, so I get not to do it, but wouldn't there be an alternative to draining 100% of the water? Couldn't you just add enough chlorine to burn up the bromine bank that you added from the spa water, then be back to a chlorinated pool? I mean, a bromine bank isn't forever lasting, is it?

Bromine doesn't "burn up". It breaks down slowly over something like twenty years. There is no practical way to get rid of it other than 100% water replacement.

Jason,
Could you expand on this? Curious what you mean. Please do not misread that I am questioning your point, just wondering what this means in practical terms. Would it mean you would continue to get false Cl2 readings? Something else?

Interesting stuff. I guess I'm a little confused about people talking about going through their "bromine bank" if their water change interval is too long.

Here is a great write-up from poolsolutions.com on the subject

http://www.poolsolutions.com/tips/once- ... -pool.html

Bromine comes in two forms: bromine and bromide. Bromine is the active form that sanitizes the pool. Bromide is the inactive form that just sits in the water waiting to be reactivated. When you add chlorine the chlorine very quickly gets used up turning some of the bromide back into bromine. When the bromine gets used up from sunlight or sanitizing the pool it turns back into bromide.

Bromine can not be stabilized against sunlight nearly as well as chlorine can be. So bromine breaks down into bromide more quickly that chlorine would (assuming you are following our recommended levels, unprotected chlorine breaks down even more quickly). That mean you end up using more chlorine to maintain a bromine pool than you would a chlorine pool.

In a spa you can use up your bromide bank through splash out fairly quickly, because a spa is very small compared to a pool, but the amount of water carried out by a person getting out is the same in either case. In a spa, a couple of people getting in and out over a few weeks end up carrying off a fair bit of the water, reducing your levels. In a pool that is a far far slower process because there is so much more water to begin with.

Aaahhh. Thanks dman...I am enlightened. Appreciate it very much.

Thanks Jason, I appreciate you explaining it. Enlightened further. Much appreciated.

Ditto, thanks!

So, suppose this UNenlightened idiot (me) put about 20 gallons of brominated water into my chlorinated pool. Would that little into a 25k gallon pool make it a bromine pool now?

20 gallons in 25,000 is more than a 1000 to 1 dilution. That will probably result in a negligible bromide/bromine amount. However, it's not based on your bromine level, but your bromide bank and that could be high if you not only added sodium bromide initially but also used bromine tabs. Even so, it's probably not more than 100 ppm so after dilution into the pool would be around 0.1 ppm.

Bromide goes away only through water dilution, similar to other salts. Bromine can outgas from the pool somewhat, though does so more slowly if you've used bromine tabs since they add DMH that acts somewhat like CYA if the concentration gets high. Bromine can form organic bromamines that may get filtered out in some cases. However, you can't really count on these methods of reduction as they could be very slow.

Thanks for the info. Thankfully, my FC seems to be pretty stable and I'm not losing any more than usual through the day. So I think I'm safe. No more spa water into pool water action though, I promise.

What if you go from a bromine hot tub directly into a chlorine pool? Are you doing basically the same thing with the same consequences?

When you say "go from" do you mean you are soaking in one and then getting out of the spa and then into the pool? Yes, it is similar except you are transferring MUCH less water when you do this -- a negligible amount.