What RO Unit are you using Brice?
If you follow what Lexinverts stated on the first page, using 100% RO remineralized to the proper TDS, using a good buffering substrate, you should be golden. Of course that's only if your RO unit is working the way it should be giving you RO that's around ph 7 and tds 0-5. If you're getting 12, either you have a cheap RO unit or your cartridges just need replacing.
A bit of both is at work. I do have a cheap unit, but it has worked well for my neos and I've been very pleased with it. (yeah yeah, I know, you don't need it for neos, but I feel better with RO water anyway.)
And yes, my cartridge prob does need replaced. I find I can only go about 4 months before replacing the filter due to my rock hard tap here.
I've not tried any buffering substrate yet. I'm basically setting myself a plan so I can get things figured out for more expensive caridina shrimp. The downside is that I don't have a lot of finances to spend, so trying to figure out how to do it on the cheap. I know now that I can line the wall of a tenner with double sponges and avoid a canister for awhile. I'm pretty darn sure I'm going to have to use a good (=$$$) buffering substrate though.