Thanks JayC, I may order the stuff so it is here so that I can do it without delay IF/WHEN something goes wrong or is obviously not right.
The Soil is JBL ProScape shrimp soil and it was set up a year ago, forgot that point! Also the tank PH was 5.5 for the first months so as you say maybe I used too much, however the new betta tank is smaller and I used a 3L bag and actually it turns out the deeper substrate look is growing on me??
Thanks again JayC, I will heed your advice, all the other parameters are perfect and there is zero problems with the shrimp (as far as I can see anyway) so I will probably just buy spare soil in preparation and store that (unopened) somewhere in a dark cool cupboard so I have it for I|F/WHEN necessary!
Bertie the betta also doing really well, active and curious thanks to your advice from the start of that project.
Simon