the only thing that evaporates is water, thus top-offs with RO
water are the best.
However, what you did wasn't a top-off, you did a small water change and replaced with freshwater because your SG
was too high. With true top-offs, SG
stays stable. Depending on what you have in the tank, you may need a 2-part calcium/alkalinity system to maintain good levels, but that's really only important if you've got a reef setup, where the corals and inverts need specific level ranges of calcium and alk
If you just have fish or fish & live rock, calcium and alk
aren't crucial parameters to maintain...your normal water changes should keep them at sufficient levels for coraline growth.