Keeping a saltwater tank in a basement suite??

[naesco]

Use one of those fridge icemaker connexions and tee it into the nearest cold water pipe.
Water goes into to ro/di than into 2x1x1 tupperware type container with a float valve and auto top off. All of which is under the tank with the sump

[Myka]

For a 90-gallon tank you can use two Rubbermaid Roughneck 18 gallon totes. One for RO/DI water and one for saltwater mixing. They fit into standard closets. I used to run my RO/DI hooked to the kitchen faucet on a timer to fill up 5-gallon pails that I would dump into the 18 gallon totes. If you have a fairly fast RO/DI then it doesn't take all day.