My pH for my tap water is 6.5-8.5 and I also use API stress zyme, stress coat, accuclear, and tap water conditioner
Every substance we add to the tank water gets inside the fish by osmosis through all the cells and via the gills. These substances then enter the bloodstream and internal organs. While they may not outright kill the fish (some can though) they still affect the fish detrimentally to varying degrees. So it is always best to use as few additives as possible, and only at amounts that are absolutely necessary for the issue.
API Tap Water Conditioner is an excellent product, and in my view the best conditioner available. Use it as directed, never adding more than the amount required for the fresh water being added.
Accuclear is a dangerous substance; it clarifies the water by sticking microscopic particulate matter together so it can more easily be removed by mechanical filters. Problem is, this also works on fish gills. Do not use this, or anything similar. The water will be clear if filtration is adequate and the fish load is no more than what the system can support and they are not overfed. Water changes and substrate vacuuming will also effect clearer water.
StressCoat is not advisable. The water conditioner aspect (removing chlorine and chloramine) is repeating what the Tap Water Conditioner does, so that is wasted (and getting more inside the fish). The so-called artificial slime coat restorer is nonsense; it contains aloe vera which is now believed to be damaging to fish gills the more it is used. Do not use this product.
StressZyme is not necessary. It claims to contain live bacteria "to consume sludge and reduce aquarium maintenance, keeping your aquarium clean and improving the natural aquarium cycle." This is frankly nonsense. A healthy biological system, improved by our careful stocking and feeding of fish, significant weekly partial water changes, vacuuming the open substrate areas, keeping the filter well cleaned...this is what you want. Live plants especially floating also benefit.
Now to the GH and pH. Presumably a GH of 3 would be degrees, 3 dGH or 3dH. This is soft/very soft water. Ideal for such species as you have. There are many suitable fish for this tank, I'll come back to this.
The pH of 6.5 to 8.5 is a real concern. If the pH is actually fluctuating this much it is seriously dangerous for fish. All those additives might factor in, along with water changes if too few or insufficient volume. But we need to pin this down. Do you have a pH test kit, and if yes, which one and type?