help choosing waterline diameter for "automatic" water change

[undbulsu]

I have fairly easy access from my basement RO/DI and mixing station. I plan to run two independent lines, one from my sump to the main drain of the home and one from the saltwater storage tank to the sump. Each will have a pump to facilitate water transfer. I plan to run PEX tubing as that seems to be the easiest for me to install. What diameter waterline would you recommend? It comes in 1/4, 3/8, and 1/2 inch. I have included a small diagram to explain things better. The total height from the basement to the sump will probably be about 10 feet and will include a horizontal run of about 20 feet.
Thanks

 

[Member No. 1]

Do you plan on a constant water changing or do you want to drain "X" gallons and refill? If constant then ¼" would be fine as I use this size with my Litermeter pump as an ATO from the basement. 10 feet up and 15 feet over. I do about 1½ gallons a day replacement.
If on the other hand you just want to drain 10 gallons and replace, then go with the ⅜ or ½ inch. I do this from my FSW mixing station in the same location in the basement. Works great!