Thanks for the explanation, jseyfert3. My PH was up to 8 again today, probably as a result of all of the aeration I did yesterday. I let the jets run in the hot tub for a while yesterday. Today, I'll just use my homemade fountain. I have some advice for thinking through how to address the stains as well.
Just curious, since you seem to have thought through all of the chemicals a lot. I'll stop worrying about the TA. But it just feels like I need to do something when my TA was super high and so was the calcium hardness (800). Would you not worry about that as well? I saw you mentioned the CSI calculation, which I read about yesterday. It felt like too much work at the time. I thought someone would have a formula and I'd just enter my numbers. But I never saw a formula.
Any advice is appreciated.
I have thought through things. I got very focus on things that are new to me and read obsessively about them. So it wasn't enough for me to follow the directions on setting up our spa when we got it, I proceeded to spend hours and hours on my tablet reading various threads here on TFP. But don't confuse me for an expert on here, there are a few of those.
As Marty said above, PoolMath is what we use around here. Plug in the numbers, and it spits out the CSI (among other things). The quick rundown on how to use it. Type in all your values from your test results on the left, or "Now" column. Near the bottom you'll see CSI calculated. Two values, one in the left "Now" column and one on the right "Target" column. Be sure to set all the values in the Target column to match the Now column to begin with, then start changing values in the Target column to see how it will afect your CSI. At a minimum you'll want to keep that between -0.6 and 0.6 as it indicates, but between -0.3 and 0.3 is better.
Along with the CSI, you'll also find that PoolMath will tell you how to adjust a given parameter (take it from Now to Target values) by adding such and such a chemical, or replacing water, etc.
The PoolMath phone app can do the same thing, and if you pay for the subscription version ($10/year) it will log all your test results and chemical additions. You can share it to the forum, which can assist other in helping you by giving them a good picture of what you're doing. To see that, if you're on desktop, hover over my username, you'll see a box pop-up and there's a "Poolmath Logs" button. On mobile simply click my username to bring up the pop-up box. You can see my logs from balancing my spa since I just brought that back online, and once I get my first pool up in about a week, logs from that as well. It works a bit differently than the desktop version of PoolMath but I quite like it. Much easier than keeping a paper log like I used to.
Anyway, the bottom line is there is not a hard and fast value for keeping TA/CH etc. It depends on a few things. For me, with a vinyl spa (and soon vinyl pool), the only thing I care about is a super high CSI, cause that can cause calcium scaling. If it's super negative, I don't care. For you, having a plaster pool, you have to keep it between -0.3 and 0.3, as too negative means calcium starts leaching out of your plaster (eating it). CSI is largely determined by pH, TA, CH, and water temp, though there are other items that affect it (play around with the Target values in PoolMath to see what has an affect). In your case, you have a high CH. The only way to lower CH is to drain and refill with water that has a lower CH. CH builds up over time due to evaporation, it typically comes out of the tap at 50-350 ppm. You can measure your tap water to find out (I'm roughly 375 ppm here, but I got a bit sloppy in that test and probably put in a drop or two extra). As the CH keeps climbing, the only way to keep the CSI under 0.3 will be to keep the pH close to 7.2 and perhaps drop the TA.
If you don't need to drop the TA to keep the CSI low, then the only reason to drop it is due to rapid pH climb from aeration. Since you have a hot tub connected to your pool, as you're finding out your pH is climbing fairly quickly. This could be a reason to lower the TA. The lower the TA, the slower aeration will cause the pH to climb (within reason). Generally, around 50 ppm TA and the pH will not climb with
any additional aeration. This is why for standalone hot tubs the TA is brought down through acid/aeration on initial fills. For pools with no spas or water features, the aeration is so slow that once a week acid additions keep the pH in check. You're somewhere in the middle, having an attached spa your pH will climb faster than a pool if you're running your jets with bubbles, but slower than a standalone spa.
In the end, it's really up to you where to put the TA. Seems like it's rising fast enough now you may want to knock it down a bit, but you'd probably be fine just checking it after each time you use the spa aeration and adjusting it at that point.
I know I'm rambling a bit, and it may not be easy to follow my thoughts here, but I hope this is still useful anyway!
