Excellent, sounds like you're making progress. Maintain, maintain, maintain is key to a SLAM. Brushing is also very helpful, along with ferreting out the algae hiding places.
There are a couple of reasons for higher CYA in a salt water pool. The easily defended reason is because it reduces FC consumption, which enables shorter run time and longer cell life. If SWG bubbling contributes to increased aeration (not everyone agrees on this), then shorter run time would also reduce acid demand. Manufacturers have traditionally recommended higher levels because they see higher FC output at higher CYA with the same electrical energy, suggesting better efficiency in the cell. But no one can explain that phenomena chemically, and experiments by a member here suggest this does not occur, so it's generally ignored. Some manufacturers no longer suggest the higher level in order to align with typical industry recommendations, but many SWG manuals still suggest 60-80 ppm CYA.
No, raising CYA to 70-80 ppm is not critical, it's just the best recommendation available, because it reduces cell run time. You can run a salt water pool effectively using TFPC principles as low as 30 ppm CYA. Below that, it's very hard to know the CYA level because the test is unreadable below 30 ppm CYA. Conversely, some TFPers without SWGs also use a higher CYA level to reduce their consumption of chlorine, but they know why they're doing it, and the risk if they need to SLAM. Further details can be found in a thread I'll link at the bottom of this post.
For TA reduction, you have three broad options. At high TA, many people find it challenging to add acid as often as required, so they lower TA, which slows down the pH rise. If the water is causing scaling, then TA reduction may be the best way to get the water balanced.
The first option is to ignore it, balance the water by keeping it at a lower pH, and add acid as often as necessary to maintain the balance. TA will come down over a relatively longer period of time.
The second option is to drop pH to 7.0 or 7.2 each time acid is added. TA will come down a bit faster. Call it medium speed TA reduction.
Or you can do it all in one or two days by dropping the pH to 7.0, aerating to bring it back up to 7.6, then acid back down to 7.0, aerate again, and repeat as needed. This is the fastest method, and is described here:
Pool School - Lower Total Alkalinity
Over time, approximately the same amount of acid will be needed to achieve a particular target TA using any of the three methods. But the sooner TA is down, the sooner that you would be able to stretch out the time between acid additions.
This thread may break your brain (it sure does mine!), but there are well-labeled sections that provide the in-depth why's
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Pool Water Chemistry
