Sorry I missed this one, Fishyshawn Welcome to TR.
For a 24 gal. ( which after sand and
lr is closer to 18 Gal.) start with just doing weekly water changes. If you think something is off test first. If you are not testing before you dose any supplement you can overdose your tank very quickly sence you dont have the large volume of water to dilute it. Plus with the smaller volume of water, water quality is much more importante. water changes being the best way to remove excess nutrients and
detritus.
IMO Supplements are for in-between water changes on larger tanks, and large bio loads. Two things we dont have in Nano tanks ( unless you are stocking fish)
As far as which salt to use. I have tryed Instant ocean, Tropic Matrin, and oceanic. None seem to be beter than the other, so the best rule is if your corals are happy with it use it.
