Dilution of the pool water is the only way to lower the CYA though sometimes you get lucky and it drops over the winter (which may or may not convert to ammonia creating a huge chlorine demand).
No, nothing has changed -- Trichlor and Dichlor always follow the rules I gave since they are related to the chemistry and not concentration of product. Perhaps there was less winter and summer rain overflow that in past years might have diluted the water more. Or perhaps more algae nutrients (phosphates and nitrates) have accumulated in the pools.
To prevent algae growth, you've got several choices. The most straightforward and least expensive is to use unstabilized chlorine such as chlorinating liquid or bleach and maintain the appropriate FC/CYA ratio. However, this requires adding chlorine every day or two unless you have a mostly opaque pool cover in which case you can add it perhaps twice a week. You can automatically dose by using The Liquidator
or a peristaltic pump or a saltwater chlorine generator. With these techniques, you should not need any regular shocking of the pool.
If you are willing to spend more money and can only service your pools weekly, then you can have Trichlor in a floating feeder or inline chlorinator and use a weekly algaecide such as PolyQuat 60 or you can use a phosphate remover (doesn't work as well if the pool is high in organic phosphates) or add 50 ppm Borates (boric acid) to the pool. You could use a copper-based algaecide, but that can stain pool surfaces and turn blond hair greenish.