I'm thinking of ordering that "Salty Shrimp - Shrimp Mineral GH/KH+".
My only concern is, does it also have all the needed minerals for my plants?
Edit - If I was to use my tap water, what kind of GH should I be aiming for?
WOW, that's hard water all right! Amazing how different it is to mine as probably only about 25 miles between us????
You were right to use RO water so at least you have a good starting point from here in! The PH may be the biggest issue as remineralising with a shrimp specific GH/KH+ will sort everything else with RO water. Cherry shrimps are pretty tough and adaptable so will tolerate PH below 7 but the nearer you can get to 7 the better, and a long time acclimating the shrimps using a dripper (there is a tube with regulator sold by ProShrimp for about £10 I think if you don't already have something) will be needed! The soil will take longer to loose its PH buffering ability with the RO though!
There are a number of ways you can go from here:
1) RO water plus a GH/KH+ and try to get the PH up somehow although you will be fighting the Soil until that exhausts its buffering ability.
2) You could mix RO and (dechlorinated) tap water at 3:1 and then use a GH+. I do a 50/50 'similar' (half tap water, half brita filtered water) on my oldest tank. can't even remember why but I believe in 'don't try and fix it if it isn't broken' so have just carried on ever since. The mixed water would start at PH 6.2, TDS 70(ish), GH just over 4, KH just under 4 and then you can mineralise it (GH+ only) for the rest. This will exhaust the soil buffering quicker than 1 above and you will save a bit on RO water, use less (about half as much) mineraliser etc. You may think this is a bit too fussy a route though, and the soil will still buffer anyway, just not for as long as all RO water, and when it stops buffering you will have a PH closer to the ideal for the shrimps.
Probably where you are now I would just get the snails for now until you have stopped adjusting the water or at least decided where next, probably not much longer before you get shrimps. I would also try turning off the CO2 and just see if it is really needed, if it looks like it is you can easily turn it back on then, but shrimps will do better without it and it MAY not be needed, same for fertilisers???
At least you are doing all this before getting the shrimps, very smart as most of us have learnt the hard/wrong way................
It looks like you will have the full set of tests when you have the GH and KH as you have the PH and TDS already! You will want the full set if you get into shrimps but once up and running you won't need to check all of them very often!
If you only order something small or one item from ProShrimp often the postage is free and stuff always arrives quickly, all my orders have arrived next day.
Last time I checked, my tap water was PH 7.5, TDS 167, GH 4-5, KH 2-3 so almost ideal for cherry shrimp (maybe a touch higher GH, which would also increase TDS, with a bit of GH+). Be interesting to see what yours is as you are relatively close, I grew up around Maidstone.