Water change amounts from startup to normal maintenance

[Seawitch]

Even if you dont do water changes frequently you probably still need the ability to at least do it once in a while so you will still need to spend the money on things like salt, mixing buckets, pumps, hoses siphons etc etc

If you are not doing water changes I could see it being a big cost savings on salt and RODI filters are such.

Even if you evolve into a no-change system, you still need things like salt, mixing buckets, pumps, siphons, and hoses, etc. etc. If you're not curing live rock in the DT, you have to cure it somewhere. Some people elect to cure it in another room or the garage. You'll have to do plenty of water changes for that, like 2x/week for several weeks. You'll have to fill and refill quarantine tanks and hospital tanks. You'll still need the RO/DI. Sometimes things like anemones spawn and make a mess in the aquarium, and you have to do lots of water changes asap that you didn't plan on.

So, for the sake of discussion, if you are doing water changes, once the aquarium is stable, figure on a minimum of 10-20% per week. Some people automate this and change a few percent per day.