i thought water restrictions were lifted? In any case, i hate wasting water too so i route my RODI waste water to my pool and/or my outdoor plants. I think as long as you're not draining it down your driveway no one is going to complain. regarding SW, there is a possibility that the LFS is using less than optimal RODI and isn't mixing properly, but salinity "consistency" isn't due to the salt . It's affected by how much water is added. (if you wanted to get technical you could argue that you could get different levels of salinity for a fixed amount of salt by weight and water by volume btw different batches of salt and btw different brands but the difference are negligible, at least to me). I have to constantly check and adjust my salinity for every batch of fresh SW i make. Sometimes i start from scratch, sometimes i still have anywhere from 5g to 20g left in my mix container when i fill with RODI and sometimes i don't top it off all the way. Because of these variables I use this calculator to figure out how much salt to add for my given water volume, currently salinity and target salinity.
Aquarium calculator; Estimate the amount of solid salt required to raise salinity to a target level.
www.hamzasreef.com
You mention you're not happy with IO and having to "dose more" VS Red Sea. It looks like you have mostly LPS and not necessarily heavily stock at that. what parameters are you checking/testing and what are you having to dose more of? I know IO Ca levels are lower than "reef" specific salts but it should be plenty fine for what you have especially if you're supplementing/dosing
For what it's worth I used IO back in the day and never had a problem that i could specifically point to the salt. I am currently using and having good success with Reef Crystals and have an SPS dominated tank and dose 2part (TM hybrid balling). Interestingly, i recall reading some people/vendors using IO/reef crystals exclusively because it IS the most consistent salt batch to batch. Not sure how true that it is. Bottom line everyone will use the product they're comfortable with and feel they're getting the best results from. Could i get better results from using a more expensive salt? Maybe, but im not is a rush to switch.
How's the QT going?