At very high CYA levels, of around 150 ppm or more, there is some evidence (see this link) of getting plaster damage. Other than that, the issues of high CYA seem to all be related to needing higher FC levels to get equivalent disinfecting chlorine concentration.
There are some problems with the high CYA / high FC approach, though it may result in lower chlorine consumption. With high FC, the pH test is not as reliable or is certainly trickier to read. Also, if one ever needs to shock the pool, it takes a ridiculously high amount of chlorine to do so -- using Ben's "lower than chem geek's FC" recommendations for shock level at high CYA would still probably work, but they might take longer to clear algae. Finally, we don't really know the full affects of high FC other than in the pool water environment. For example, drinking the water would result in more total chlorine intake, though even "first symptoms" levels are far higher than what we are talking about here. Water evaporating on swimsuits drying in the sun may get affected by the total FC level in terms of total bleaching potential, even though it would be rate-limited by the CYA -- I'm not clear if the chlorine outgasses or if it forms solid Trichlor/Dichlor or what, but it COULD bleach more when concentrated through evaporation in the sun -- I just don't know. Same principle might apply to skin and hair in terms of drying or brittleness, but I'm not sure.
Richard
There are some problems with the high CYA / high FC approach, though it may result in lower chlorine consumption. With high FC, the pH test is not as reliable or is certainly trickier to read. Also, if one ever needs to shock the pool, it takes a ridiculously high amount of chlorine to do so -- using Ben's "lower than chem geek's FC" recommendations for shock level at high CYA would still probably work, but they might take longer to clear algae. Finally, we don't really know the full affects of high FC other than in the pool water environment. For example, drinking the water would result in more total chlorine intake, though even "first symptoms" levels are far higher than what we are talking about here. Water evaporating on swimsuits drying in the sun may get affected by the total FC level in terms of total bleaching potential, even though it would be rate-limited by the CYA -- I'm not clear if the chlorine outgasses or if it forms solid Trichlor/Dichlor or what, but it COULD bleach more when concentrated through evaporation in the sun -- I just don't know. Same principle might apply to skin and hair in terms of drying or brittleness, but I'm not sure.
Richard