Water changes are how I always reduced my TDS, as I usually don't vacuum. I use just RO with no prime.
If you are taking water out, you have to put water back in of the proper gH, otherwise you are also dropping your gH as well as your TDS. You want to keep your gH constant, while lowering your TDS. You should always remineralize your water unless you are just doing a top-off due to evaporation.If you're using a product to raise GH you are also raising TDS (possibly). I know for a fact Fluval Shrimp Minerals while easy to control how much GH you raise, it will shoot TDS through the roof. Sent me TDS meter off the charts saying 450 with a blinking "times/X 10" . I know you said it was nothing but RO and Prime but for the folks suggesting get your GH where it needs to be, they may be failing to realize(or forgetting) it will also shoot TDS up.
Pretty sure I've tested RO water after adding Prime and haven't noticed any jump in TDS but won't swear to it.
If you do the math it makes sense. You have 8 gallons of water at 287 TDS. You changed out 1 gallon. 287 divided by 8 equals 36 (so, say 36 TDS per gallon). So for each gallon of water you change with straight RO it will lower the TDS by 36. 287 - 36 = 251. Pretty darn close to where you wound up.
Lol! You really think I wouldn't know that? Heheeeee!folks suggesting get your GH where it needs to be, they may be failing to realize(or forgetting) it will also shoot TDS up.
Ummm...no, that's not what I meant. But someone is asking about how to lower the TDS and you brought up remineralizing to deal with GH and did not bring up that it will also raise the TDS of the water. At least, nothing in your posts suggests to someone like me (that's not an expert in all things shrimp related) that it will raise TDS. So I just think that both things need to be clarified when they are going to be suggested. I've seen it mentioned time and time again by other posters. Folks have to learn...I'm one of them. I bought some Fluval Shrimp Mineral expecting it JUST to raise GH since that's ALL folks brought up on here is it just does GH, not KH, etc, etc. Nobody mentioned the massive TDS increase. And for newer folks to the hobby such as myself still trying to figure out all the parts of water chemistry that are important in shrimp keeping, I actually prefer things be spelled outLol! You really think I wouldn't know that? Heheeeee!
I believe it makes sense when they say that GH and temp should be matched to the tank.
I know what TDS stands for and I know it doesn't break anything down into what each 'dissolved solid is'. But when I deal with MY water and how I mix it (certain parts tap to certain parts RO) then I pretty much know that everything else is going to fall into the same areas as the tanks because it's the similar proportions to what my tanks are set at. When I get the TDS to measure close, everything else falls into place FOR ME. When I was setting up my last tank, I tested the water in the tank, tested the water I was going to put in the tank for changes and once the TDS got close, so did the KH and GH and pH was only about .2 higher when I put it in (would drop in a few hours). I'm not raising low pH shrimp so it's much easier for me than someone trying to raise high grade crystals. And as far as acclimating, there really isn't enough water in the bags I get shrimp shipped in for me to test GH, KH, and PH (using drip tests) so I try to get the TDS close. It's just what I do. Didn't say it was right or wrong, I'm saying I do it differently than some folks and so far it has worked out fairly well for me and the species I keep. Could just be dumb luck. I'm still trying to learn how everything correlates to the other (the relationship in KH, GH, TDS, etc if/when there IS a relationship).TDS is just total dissolved solids, doesn't tell you what it is or it's proportions.