Spa Question

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Yes...we did have scaling in the spa previously, which was a PAIN. I'm glad to hear that a negative CSI will work.

You bring up a good point. I'm guessing the spa probably isn't vinyl. Our pool is vinyl but the spa is probably fiberglass or something of a hard shell similar to what boats are made out of. I have no idea about gel coat. I inherited the pool and spa when I got married. My husband was a bachelor living here for 10+ yrs before I met him and he bought the house for the pool and then purchased a spa to complete the "bachelor pad."

I will keep the CSI number for pools in the back of my head; especially since our native water seems to have both high TA and high CH. Speaking of which - I am currently aerating the pool in an attempt to avoid scaling. I found our TA had drifted upwards recently and the Calculator indicated we were at risk of scaling (I don't recall what our number was, exactly. I have NO desire to scrape scale from pool walls, so we are at the tail end of an acid/aeration cycle.

I ran the numbers to see about adding 50ppm of borates to the pool to help with all this. Calculator told me I needed something like 76 boxes of Borax! What?! That's crazy volume.

Anyway - thank you so much for all the help these last few days.
Molly
 
Yes, 50 ppm Borates is a large volume, somewhat similar to that of 300 ppm Calcium Hardness (the reason it seems different is that the borates are measured as ppm Boron with molecular weight 10.8 g/mole but in the pool water it is mostly boric acid with molecular weight 61.8 g;mole so 5.7 times greater in weight). You can use either Borax and acid or can get boric acid directly. It's certainly optional and not required, but some people like it -- I have it in my pool.
 
So, the party is over. We had 18 guests. The pool, spa and fire pit were all brilliant.

Testing the spa this morning I found:
pH 7.4 (yay!)
FC 4
TA 60

Questions: Do I need to lower TA, once again, back down to 50? and why did it rise?

I added 2oz of bleach to take FC back to 5ppm but was I supposed to shock the spa after so much use? I had it at shock level PRIOR to everyone arriving and was pleased to at least see there was still FC this morning. Just wondering if I was supposed to shock today...?

Also - with the pool: it, too, was at shock level (12.5ppm) prior to the party and this morning it is only down to 11ppm. Shouldn't it have dropped more?

Thanks,
Molly
 
I wouldn't worry about the TA. It's close enough, especially if you find the pH to be fairly stable.

Keep an eye on the FC level. It may still drop faster than usual due to the high bather load you had. You don't have to shock the spa. Normally, when it's just you or your family in the spa, you start out with a low FC, perhaps around 2 ppm, then after your soak you add chlorine to handle the bather load. With your guests, you added more chlorine up-front so don't have to add as much afterwards. So what FC did you have in the spa before the guests started using it?

As for your pool, the volume of water is so much larger that the bather load isn't as noticeable. Every person-hour of swimming in a 36,000 gallon pool only results in a chlorine demand of 0.03 ppm so even with 18 people swimming for 2 hours, that's only about 1 ppm FC. So you say 12.5 ppm FC was in the pool and this was shock level, so you have 30 ppm CYA in the pool? I thought your CYA was higher than that. Is the pool exposed to a lot of sun? If so, then if you find the chlorine loss is high during the day, you can increase your CYA some, perhaps to 50 ppm. When you aren't using the pool, but it is exposed to sunlight, what's your 24-hour FC loss in percentage terms? Do you have a pool cover?

By the way, in the future, especially for the pool, you don't need to go up to shock level before a party. Just a little higher than your usual is sufficient unless you have lots of kids urinating in the pool and even then your pool is pretty large so unlikely to be a problem. It's more pleasant to swim in the lower chlorine level. So no one complained or noticed the higher chlorine level in the pool or spa? I would think they would notice if you had it at shock level.
 
FC in the spa before guests started using it was at 12ppm. The spa was used from 7:30pm-10:30pm with anywhere from 2-6 guests at a time and a few times sat empty.

I was concerned that people might not be comfortable swimming/soaking in such high FC, but was going on what I thought to be the recommended level to high bather/swimmer load. Thank you for clarifying that I don't need to go that high "next time." No one complained about the chlorine - either no one noticed or everyone was very polite. I've no idea which one is the truth. I didn't swim or soak personally.

The pool has a CYA of 30 best I can tell. I tested it yesterday, expecting to find a higher number. I'll be the first to admit I hate that test. I swear I can see that dot no matter how much fluid is in the chamber - no matter which direction I stand or if I'm in sun or shade. But 30ppm is my best estimate.

24hr-loss of FC is very slow. I lose 1ppm of FC every 48hrs. Our pool gets full sun (10hrs of sun) and we do have a solar cover (I forget how many mils). Since we've been getting a lot of rain - we're trying to generate warmth, it's been hovering around 82 and getting to 84 by the afternoon.
 
OK, your situation sounds good and well under control. Congratulations on have a successful swim party. Next time with a lower starting FC you'll likely get comments like "how do you keep the water so clear? I don't smell any chlorine."

The chlorine level you started with in the spa, if it was at a hot 104ºF, was equivalent to 1.7 ppm FC with no CYA so higher than we normally use, though still more like what you'd find in commercial/public pools that don't use CYA. If you instead start with something like 4 ppm FC, then that's more like 0.5 ppm FC with no CYA or 2 ppm FC that is more like 0.25 ppm FC with no CYA. Hot water has less chlorine bound to the CYA and it also has chlorine react faster and chlorine and monochloramine outgas faster. So for people using a spa for themselves, they normally start with a low 1-2 ppm FC and then dose right after their soak with enough chlorine so that they end up with 1-2 ppm FC again the next day (for their next soak if they soak daily).
 
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