ya i've been looking into a used refractometer but honestly i don't think that SG has to be super accurate for coral health as long as it's consistent

I give up

Well, it has to be consistently accurate. Now adding straight RO to your tank kinda drifts away from this theory, dontcha think?

What matters is that you tried....


Ok, here it is -
Regardless if you are using a hydrometer or a refractometer:

1. When doing a water change, test your aquarium water's SG, then mix the replacement fresh water with salt to match this SG number. It does not matter if the water you are mixing the salt with is RO/DI or tap water - it will not make a difference in your SG levels. If you do this your SG will not fluctuate (by anything significant) during a water change.

2. When doing a water top-ff due to evaporation, DO NOT mix salt water for this, just use straight RO/DI fresh water and top off to the SAME level in the aquarium before the evaporation.

3. An SG reading between 1.023 to 1.025 is good. I would consider 1.021 too low.

It sounds like you need to pick a set point of specific gravity for your tank, and then read up on how best to maintain it. I'm not sure if your confused between topping off, and water changes, or if you just don't understand them out right.

Watch this ---> http://www.youtube.com/watch?v=kSTY346rros

In short, if your confused please ask. Many of us here are more the willing to help you out and get you pointed in the right direction.

-no theres nothing alive, cause i just love growing cyanobacteria and hair algae for fun..

what ever all my fish and corals are growing great so no complaints so far, mind you i always do little water changes so the SG doesn't even go up or down really, just happened this time because i did a big w/c

I think the point people are trying to make here is that your logic, regarding water changes, thus far is fatally flawed.
I haven't seen a light bulb go off over your head with respect to your first couple of really ummmm.... unconventional posts concerning SG and water changes.
Read between the lines..... you could do a 100% water change and not change the SG.........

-ok ok i totally screwed up but it never caused absolutely any harm to any of my livestock so as you can imagine i never really made a big deal of it, but my w/c's are always small

Ergo, it's a top off......
Not a water change.......
Unless you're taking water out of the tank and replacing it with RO/DI water......
I don't even want to contemplate that gong show........