I suspect Dsetz has pinpointed the issue here.
My favourite substrate is very high with minerals etc and when new they advise 50% water changes every 2-3 days for the first 2 weeks to avoid a build up of minerals when first used, so this may be what has happened here. Adding fertilizers will obviously add to this as well?
The neocaridina shrimp should be fine as long as you make any changes slowly, but they probably won't be too happy until it gets nearer their usual accepted ideal parameters. Just keep changing the water with RO/distilled water to slowly bring it down and the soil should deplete of the excess minerals with time. I wouldn't expect that you need the fertilisers at this point either with new substrate, or maybe even at all depending on the flora you have in the tank as the substrate should have that covered?
It may be worth getting an RO unit long term as even when you get to the correct level your tap water is too high so you will either want to mix 50/50 tap/RO, or 100% RO plus remineraliser?
Simon