I don't have time ATM to answer with a super complex reply, but I know I went "huh??" when I heard about the 5x dosing to eliminate nitrite. In my ancient bottle of Prime (I estimate about 3.5 years old, brought it over from when I lived in an apartment with municipal tap water vs. house with dechlorinated well water) I only see a mention of detoxifying AMMONIA not nitrite, in an emergency, by doing 4 drops per gallon.
I've never added Prime to the main aquarium. I know people do, when they do water changes with Pythons and such. But I've always done water changes with buckets, so I've never added Prime directly to the tank...and even though there is no mention of it being unsafe to do so, I wouldn't, because if you smell the stuff it reeks of sulphur. So I don't want that going straight into my tank!
DeeDee, I think it would be beneficial for you to do your water changes with seasoned water. Get a 5 gallon bucket, fill it, and drop an airstone in it. It costs next to nothing to get a used air pump rated for like a 10 gallon tank, and the Whispers and Renas are quiet enough not to be annoying. Add your Prime to the water and let it sit for 24 hours. (You need the Prime because you have chloramine in your water no doubt, which does not evaporate like chlorine does.) Then you can change water 'til your heart's content!
I know you are not lazy...you're always screwing around with your tanks

But I think you run your tanks in an unconventional way with the infrequent water changes, if not total avoidance of them and only topping off. I think it's because you are scared of your tap water. I get it, but your water is probably very hard so your TDS must be ought of sight. This is hard on lots of fish (don't know about shrimp) so you should get on a regular schedule of small, weekly water changes. The water doesn't take away anything beneficial...the mulm, biofilm and whatever else is not in the water column. So all you are doing is diluting metabolites and TDS, which is beneficial to any species.
Shrimp keeing is new so I can see people saying stuff like "shrimp do better with fewer water changes" - kind of like the way people were in the beginning with fish keeping - using aquarium salt, carbon, UG filters and such. But the truth is, no fish (or shrimp) do better with no water changes! If they are "sensitive" fish that like "aged water" then just do small, frequent ones instead of large ones, and condition/season the water ahead of time in a bucket.