How to prepare for high user load in a Bromine spa?

[michy]

I use a bromine floater and also add 1 tbsp of brominating granules (85% sodium dichlor, 15% sodium bromide) after each use. (2 people for 15-20 minutes) Adding the granules after use was recommended by the vendor as well as another pool store to keep the bromine levels constant. So far it seems to be working. I have ordered a Taylor 2106 kit but haven't received it yet, which I plan to use to get an idea of my bromine demand. I don't trust the test strips. I have people coming over this weekend and want to know:

If 4 people use the spa for 15 minutes, do I add 4 tbsp of granules afterwards?
Should I put something in even before they get in?
Is there a calculation to figure out how much to put in (# people, amount of time in spa...etc)?
Also, can I put in MPS instead of the granules? I know one is an oxidizer and one is a disinfectant but I've heard different things.

Thanks,

Michy

 

[chem geek]

Michy,

Welcome to TFP!

I can tell you that the rough rule of thumb for oxidizer demand is that every person-hour of soaking in a hot (100-104F) tub requires about 3-1/2 teaspoons of Dichlor, 5 fluid ounces of 6% bleach or 7 teaspoons of non-chlorine shock (MPS). Your brominating granules are mostly Dichlor (85%) and 1 tablespoon is the same as 3 teaspoons so this would roughly handle 44 person-minutes of soaking or two persons soaking for 22 minutes. Lo and behold, that's about what you've been doing. Your bromine floater must be set at a very low level -- probably just enough to make up for slow outgassing of bromine.

So 4 people for 15 minutes would need roughly 3-1/2 teaspoons of Dichlor or a little more than 4 teaspoons of your brominating granules. To play it safe, you could use 5 teaspoons. Even if they were to soak as long as you do (15-20 minutes), you wouldn't use more than 2 tablespoons which is double what you use with just 2 people. I'm not sure where you got the result to use 4 tablespoons -- the 1 tablespoon you currently have been using is for 2 people.

By using the granules over time, you have likely built up bromide in your water so could use MPS to activate the bromide to bromine instead of using the brominating granules, but it would be even less expensive if you just used 6% bleach instead. When it is just the two of you, you would add around 3-1/3 or perhaps 4 fluid ounces of 6% bleach. When it is 4 people, you would add 5-6 fluid ounces for a 15-minute soak. Unfortunately, there is no good test for bromide so you can't tell when you'll need to use brominating granules again, but what would happen then is that you would essentially be in a chlorine spa instead of a bromine one. You might be able to tell the difference from the smell since bromine smells different than chlorine.

Regardless of how much you are adding, you can tell if you are adding enough when you measure a small residual of sanitizer (at least 2 ppm bromine or 1 ppm chlorine) just before your next soak.

Richard

 

[michy]

This is great info, thanks so much! This is my first spa and I'm still trying to figure it all out. It's been a little confusing, because I'm hearing different things from the manufacturer, the stores and the forums (this forum has definitely been the most helpful) I don't like playing guessing games when it comes to chemicals, so your guide will help for sure (and my Taylor test kit, when it arrives). I will give it a try and report back on how it worked out.

Btw, I think I meant to say 2 tbsp and not 4. I had the number 4 on the brain (4 people).

Michy

 

[michy]

So we were 4 people in the tub for about 40 minutes and I figured to put 4 tbsps but put in 5 tbsp of bromine granules just to be safe. Was that right? Anyways I checked my bromine levels the next day and they were through the roof - over 20ppm according to my test strips. The day after they were down to about 10ppm. And today they're at 0! Not sure what's going on there. Maybe that means my floater is set too low?
Anyways, I was due for my weekly shock today, so I shocked it with more granules. (I don't have any MPS left) Am I doing something wrong?

Also, I know this has been asked in other posts, but I now have foam bubbles when i put the blower on. Never had this before our visitors so thinking it's detergent, shampoo, etc. I've read defoamer is temporary, so what else will get rid of it?

Thanks,

Michy

 

[chem geek]

4 people for 40 minutes needs 3.5*4*40/60 = 9.3 teaspoons or around 3 tablespoons of Dichlor or closer to 4 tablespoons of your granules. I takes time for the bromine to get rid of everything introduced by the bathers, though usually it does in less than 24 hours in a hot spa. It might be that the bather load was higher due to lotions or other things the people brought into the tub. Just use some chlorine (such as bleach) or non-chlorine shock to reactivate some more bromine and see if it starts to hold the way it used to. Some will dissipate over 24 hours, but it shouldn't be as much as you are seeing.

You can reduce the amount of foaming by having the Calcium Hardness (CH) at 120 ppm or so. If it's too low, then foaming can occur more easily. You don't want the CH too high, however. Usually keep it below 150 ppm unless your Total Alkalinity (TA) is low (below 80 ppm).