Should recommended TA levels for vinyl pools (70-90); and possibly other outdoor pools, be updated and further explained in Pool School? maybe under the section about TA? or as a note under recommended levels? A more complete explanation permitting lower, natural TA levels under curtain circumstances could save many members lots of work, and, instead of each of us learning one-by-one through forum inquiries that there is an easy way to solve this problem, this high out gassing scenario could be explained and parameters given to allow TA lower than the tables given.
There are many on here with vinyl liners (and other surfaces too) that are good students of pool school. We pay attention to detail when we execute what we've been taught. But there are some on here that have found, including myself, using the pool school recommended levels and trying to stay in the range for all the levels all the time as much as possible, that we constantly deal with rising ph, and subsequently, due to the fact that we are regularly adding acid doses to maintain ph, that we're regularly lowering TA out of range through these regular acid doses. And then, as good students, we know from what the calculator shows that we're going to need to regularly test and raise back up our TA to get it back in range. But this becomes an endless cycle for those of us in this situation.
I had this problem myself...I was going out of range on ph about 4 days a week and adjusting back to mid-range with 7 oz of MA each time. About every two weeks or so my TA would fall below 50, and being a good student of pool school and knowing the recommended levels for my vinyl pool, I would immediately calculate and raise my TA back to mid range (80); not knowing that being this good student was the root of my problem. I started a thread asking if it was okay to let my ph run around 8.0, since, in my mind, the ph was the culprit and not being chemistry minded, never even thought a moment about the idea that in some circumstances TA can be allowed to settle below the recommended level.
But since being given the great advice and help by Chem Geek and others on the thread I started, I have found at least five threads with the same or similar problem, with the same easy recommendation to fix it.
Here is a quote by Chem Geek on one of these threads...The lower the TA, the slower the pH rise from carbon dioxide outgassing until you get to the point of TA equilibrium with the carbon dioxide in water and air. However, in practice you only need to lower it to the point where the pH is reasonably stable (i.e. where the regular acid addition is not huge nor annoying). Also, if you have evaporation and refill, then TA from the fill water will increase the TA in your pool so lowering the TA a lot in the pool may be a but futile. You sort of what to get to a point of balance where you add enough acid to compensate for the TA rise from evaporation and refill and hopefully the pH at this balance is somewhere reasonable, perhaps 7.7 to 7.8 or so unless you're lucky to be able to have it lower around 7.5. Every pool is different since the amount of natural aeration varies.
With your vinyl pool you don't need to saturate the water with calcium carbonate so there is not a problem having a lower TA especially if you have 50 ppm Borates for additional non-carbonate pH buffering.
This was so simple once I started practicing it. If I start with TA at 80, and I lower ph to 7.5ish each time it rises above 7.8 with MA until my PH quits rising; then my pool will settle in @ 5 drops to clear, which means my TA is somewhere between 40-50, and all these crazy adjustments go away. But if I hadn't asked or searched and found a previous post with this simple answer, I don't think I would have found it on the site otherwise. And I wonder how many are executing this endless cycle trying to be good students of TFP and not even thinking to ask if there is an easier and cheaper way to maintain PH with a higher-than-normal outgassing pool.
So this is my question and point of this thread...If the proper TA level is in reality specific to each pool to create a PH equilibrium, why is it taught to be kept in a specific range? Is it because my situation and the others I've read about are uncommon? Or is because it is too complicated to bring this strategy up in pool school and best left to resolve on the forums? or is there another answer or something I'm not understanding?