G'DAY michaelJ, thank you for the reply I was worried the post might have been a bit old to get a reply. The re-mineralizer is AZoo Gh plus gh and is according to the add, and its supposed to be new.
Hi @Kelvin12 According to the product page for AZoo GH Plus 5ml adds 1 GH per 100 L. So if your conditioning 50 L for say a GH of 6 - assuming its all RO water - you should add 15 ml. or basically 3 of the inner 5 ml caps. This will require 6 drops using the API GH Test before the water in the test-tube turns green (remember to shake the tube with the cap on a couple of times between each drop).
Your KH will still be zero. In order to raise the KH you need to add a conditioner for that. You can use a bit of Calcium carbonate (CaCO3) which is cheap and readily available of Amazon - a quarter of a teaspoon (1 gram) will add about 1 KH to 50 L. (it will also add about 1 GH - so you could lower the GH Plus dosage to 12.5 ML or two and a half inner cap if you want to remain at 6 GH...).
When you do weekly 50% water changes (25L), again, assuming all RO water, you just use half the amounts or a bit more to compensate for precipitation and uptake etc.
Unfortunately there is no guaranteed analysis on the GH Plus product, it only states its a water soluble mineral complex, so its hard to say what your resulting TDS will be, but a cautionary guess, based on the KH + GH + some minerals, is about 130 ppm. which should be perfect for Crystal Red Shrimps and still leaves a bit of headroom for additional fertilizer for your plants - not much though. Which, btw. is the reason I have not plunged into Crystal Red's yet... I would have to go lean on fertilizer and use 100% RO water... to meet the lower TDS requirements vs. Neo's... Instead of my current 40% Tap water / 60% RO water mix and lots of Macro fertilizer for my densely planted tanks.
I hope this helps!