Well, the water report doesn't tell me anything, they don't mention minerals anywhere (except lead and copper, and neither is in the source water anyway).
That substrate shouldn't cause problems, though I've never used it. I do find it a bit aggravating when they say it is guaranteed to work provided you use all their products.
You haven't posted a photo, which might help on the plant problem. Now I know that you are using Excel, that may be something. I know Excel is detrimental to some plants, especially Vallisneria. Entire stands can literally fall apart with Excel. I do not recommend this product, notwithstanding my considerable trust in most Seachem products.
Algae occurs due to light, period. In planted aquaria it is possible to not have algae issues, but to do so the nutrients and light must be balanced to provide what the plant needs, with light as the limiting factor. [I'll assume you know what this last phrase means, but if not I can explain.] One has to experiment a bit to find it, especially when using enriched substrates that are intended to add nutrients but we can't know just how much. My tank with Flourite substrate is the same. And I have algae issues in there too, due to the light and imbalance.
With those fish, softer and slightly acidic water is ideal, so there will be no issue from the pH at 6.2 and I would leave it. In any case, it is always preferable to let the tank run itself, provided it does not get extreme, and fussing with the pH will be more trouble than good. The KH at 2 is near-zero buffering, so the tank biological processes will regulate the pH and it will be low.
I am still puzzled by that hardness. That is not good for these fish. I would further reduce it as you suggest.
So, my suggestions are:
1. Discontinue Excel.
2. Further reduce the hardness with a 75/25 mix (RO/tap water).
3. Don't use the Regulator.
4. Reduce the light duration. Any way to reduce the intensity, by half? This would be preferable to achieve that balance. Also, what exactly is the light (presumably fluorescent, which tubes, Kelvin, watts, etc.); this may show something to me. And a photo if you can.