As JayC states, that may not be suitable substrate for shrimp so you should probably consider changing it for a different substrate. he Ph of 7.5 is fine as cherry shrimp are suited to that and under normal circumstances salty shrimp Gh/Kh+ is the one to use with cherry shrimp, but the combination of the substrate and the salty shrimp is compounding the parameters to go so high.
The increase in the TDS during the week may be part down to evaporation as you should top up evaporation with RO non-mineralised water. Both your sets of TDS numbers though should be ok with cherry shrimp!
In the meantime I would try not using the GH/KH+ which should help bring your parameters down a bit more towards the requirements of the shrimp (though the GH/KH+ has all the ingredients that shrimp need obviously?). You will want to slowly reduce the figures anyway even if you change the substrate so that the parameters are closer together
You may want to watch this video as it is very informative and may help you decide on where to go from here????
You should be ok using distilled water but I would do the full set of tests on some to start with just to double check, in theory it should be 0 TDS/GH/KH etc as I am sure you know? The choice of substrate is dependant on what you are hoping to keep in the tank, soil substrate if you are keeping lots of plants (though that in itself will alter some parameters), but you can use an inert substrate with cherry shrimps as they don't need the buffering effect of the soils as bee shrimps do! My cherry shrimp live in dechlorinated tap water, but as he states in the video RO water remineralised is better as it has everything in it the shrimp require?
That's due to the salty shrimp GH/KH+ which is doing what it is supposed to.
If you don't want pH to rise you need to use Salty Shrimp GH+.
That fluorite substrate needs to go.
Depending on which version of Fluorite you bought, the red or black version, flourite has iron,
potassium and magnesium and high levels of calcium and sodium present.
I have a ten gallon aquarium with bloody mary shrimp. I have been using fluorite gravel and it keeps pushing up my GH and KH. I am now changing 20% of my water every week in order to try and slowly adjust it. My GH had been 15 and my KH about 10. I now have it down to GH of 14 and a KH of about 7. I have researched this on other sites and it seems that the Fluorite gravel will gradually stop leaching calcium. I have also been reading that a KH of 8 and above can cause problems with neocardina secondary to their shells getting too hard and the resultant white circle of death. My TDS can run anywhere from 230 or 240 after a water change up to 280 to 290 at the end of the week. Ph is 7.5 and above. I am no longer adding any supplements to the water.
One more question. I am using salty shrimp GH/KH premium aiming for a TDS of 100 after off gassing as the water I change with. I am adding it slowly over 6 hours. The distilled water has a ph of about 6.4 before I add the salty shrimp. After I add the salty shrimp to a TDS of about 100 my ph increases to about 7.5.