Canister Filter Adjustment.

TDS includes more than GH.

GH just measures divalent metal ions. In practical terms, this is mainly calcium with some magnesium and trace amounts of other metals.
TDS measures everything. Divalent metal ions, mono and trivalent metals ions, anions, non-ionic substances. And it includes things we add to the water such as dechlorinator and plant fertiliser.

Using TDS rather than GH is better as it measures more.

For hardness, both ppm and dH are used. Some fish profiles use one, some use the other. You need to know the hardness in both units.

I would not use Prime. They won't say what's in it ("trade secret") but considering the things they claim it does, it's a chemical soup. Everything we add to a tank gets inside the fish so the less we add the better.

Does your water company use chlorine or chloramine? If they use chlorine, the best dechlorinator is API Tap Water Conditioner. That contains only two things, thiosulphate to remove chlorine and EDTA to bind metals. It is also very concentrated. For chlorine the dose rate is 1 drop per US gallon (3.75 litres)

Those dechlorinators which contain some thing to 'stimulate the slime coat' are also not recommended. Most contain aloe vera which coats the fish's gills. Others contain polymers which do the same.

It can be complicated at the beginning, learning all the things you didn't know that you didn't know 

It does get easier.....

See, there's always someone who can give a sensible answer.