Well Water Too Hard With So American Cichlids

Hi, I have a 110 gal freshwater tank with 3 Blood Parrots, 2 Severums, 2 Blue Acaras, 2 Kribensises, 1 Bolivian Ram, 1 Plecostomus, and 4 nerite snails.
I have a Sun Sun sump filter and I do weekly to every other week water changes of 10-15gal, and add Stress Guard and 1/4C aquarium salt each time.
1 year ago in March I moved from Southern MN to northern MN. Here I have well water and the water is extremely hard, since this winter I noticed the GH is usually off the charts high.
This area is known for having extremely high mineral content in the water and I've been told well water fluctuates a lot in the winter time. Moving up here I didn't know that and have had issues with Hexamita infections twice in the last year and overall the fish have been very stressed.
This winter is when my fish first started to appear very stressed, the blood parrots were constantly pale, at which time I realized the GH was higher than normal.
I purchased a RO/DI filter and have been using that for water changes, it seems to work great to reduce hardness - the water produced has a pH of 6.2, KH 0-40, GH 0-30. I've been using this for 3 months now and I still haven't seen much improvement with my tank water - the pH is about 6.8-7.0, KH 80, and GH 180.
The RO/DI filter has brought the pH down from 7.8 but has not seemed to affect the GH. And each time I do water changes the water changes seem to cause my fish stress, the blood parrots become pale and it takes about 1-2 weeks for their color to improve.
I'm assuming this is due to fluctuations in the pH?
Is there any thing I am doing wrong?
What can I do to improve the quality and consistency of my tank water?

 

Well you shouldn’t use just straight RO/DI water, you should either mix it with tap/well water, or remineralize it so it has at least some essential dissolved solids. Your water isn’t changing because you’re water changes are too low volume. You should aI'm for 25-50% changes once a week. If the water is a different temperature than the tank, that will cause stress.

 

I have been cautious about doing larger water changes because of the big change in pH. Should I not be worried about this? The tap water pH is 7.5 and the RO/DI pH is 6. 2, and the tank pH is about 6.5. I've kept a close eye on nitrate & nitrite levels and they are usually at zero still when I do water changes. I haven't been adding a mineral additive (such as Replenish) because of the GH being so high.

 

If you mix them and do 25% changes, it’s going to bring it down slow enough not to cause stress. Also, I would stop the aquarium salt unless you’re treating something, and even then I think it’s useless.

 

Thank you AqauticJ for you input!

 

Basically what I’ve done at home is mixed my tap with RO/DI and tested it until I got the PH, GH, KH to the levels I want the tank at. Then I use this mix each time I do water changes and slowly overtime got my water to be the same as the mix. You’re welcome