As is the case for many people here, we inherited our 12K gal. in-ground pool and everything that goes with it when we bought our house a couple of years ago. Over those two years, I've successfully eliminated the effects of most of the bad practices (floc, copper algaecide, sequestrant, etc.) and replaced the poorly maintained/mismatched equipment that came as part of the deal. One legacy remains: the AquaTrol unit. Time and again, people on this forum have asked me what the heck I'm doing with an AquaTrol on an in-ground pool. Hayward explicitly says, "AquaTrol units are not rated or recommended for in-ground pools." And so I say, why? I've never received a good explanation for it. Is it such a poor match that I should replace it with a properly-rated unit as soon as it is practical? Or should I just let it live out its days and then upgrade when it reaches the end of its life? It has performed well so far; with a T-CELL-5 attached, I only need to run it at around 15% with my VS pump running 24/7. My only gripe is that it consistently reads salt about 400 ppm lower than the true level, even with a new cell, but it sounds like that can be expected of most units.