This may be a good time to mention something about RO. I've no idea as to your level of experience/knowledge so forgive me if this is old news. But as one who has gone the route of having to prepare water for a couple of issues, it may help you decide.
First, the water for all water changes must be prepared outside the tank. I used one of those large garbage containers, Rubbermaid 30+ gallons. The GH/pH/temperature must be the same as the tank water. Next problem is siphoning it out into the aquarium; with the container likely on the floor, you are restricted to using a bucket or one of those rubbermaid fruit juice pitchers (lidless). This needs to be done for any emergency W/C's too.
Second thing is the fish preferences. If you stay with all soft/very soft water fish, like cories, tetras, gourami mentioned, I would not mess with mixing but just use straight RO. This is basically what they have in their habitats and they have evolved to function at their best in such water. They get what minerals they need from their food. I have been fortunate in my 30 years of aquaria to have tap water that was about as good as it gets to such water, zero GH/KH and a very acidic ph (below 5 so far as I knew). I let the tanks pH do what it wanted, and the biological system established in each tank and readings of pH never fluctuated over months and even years beyond more than a decimal place or two. If however you move to Central American cichlids or livebearers, this is not going to do it obviously.
Third, I used Equilibrium for three or four years in two tanks (the largest). A well-meaning member (another forum) persuaded me it was necessary (the old fable again, fish and plants must have minerals in the water, blah, blah). This was primarily to get sufficient calcium for the plants, given my water purity; the swords did show signs of calcium deficiency. I subsequently switched to using Flourish Tabs for the swords and stopped the Equilibrium. Plants didn't seem to notice, but I was more concerned with the fish. Ian Fuller breeds cories in straight RO.
@seangee uses this in his tank(s). It is in my view easier. If you do decide to increase the GH, with the fish again mentioned I would not go as high as 10 dH. Down around 2 or 3 is more than enough, though again zero is even better. Equilibrium is geared for plants, and Seachem answered my direct questions by saying it should not be used for fish, just plants, and if fish need minerals, their Replenish was a better choice. I've no idea why, I certainly did not need any mineralization for any of my hundreds of fish, so I didn't pursue it.
ON the cories, pygmies I always find get lost in large tanks. I don't mean they hide--though they do--but more they are so small you just don't see them much, especially if the other fish are not similar nano size. All cories need sand of course, I think we dealt with that elsewhere. But it is important for their health, very much so.
And in such zero GH water, fish do have fewer issues health-wise. That seems to have been my experience. The three problems I had over the last 20 years were all brought in with new fish and largely my stupidity. Give the fish what they need and they will be better.
