My wash routine is: warm quick wash w/ Calgon, hot 50C wash with Calgon and 3/4 scoop Tiny Bubbles, longest cycle, warm quick wash (no additives).
I would recommend you start with 1 scoop and see what happens. You can adjust up or down if you need to. If your hardness is greater than 250ppm, that's probably where you want to start playing with Calgon.
I think Grovia has been changing up how they distribute their products. I seem to remember a couple of years ago a lot of people were getting it from Costco online, but then it stopped being available there. My local baby boutique hasn't been able to get Grovia anything for the past year.
My current box is from an independent health food / pharmacy that was near my ILs place when we were visiting New England. You might try the store locator on Grovia's website to see if anyone local to you is carrying it. Or if a favorite online vendor has it, buy from them and build up some points.
I was having a hard time finding it, so I switched to Nellies. I like it just as well. I used to be religious about using Calgon with it, but I haven't been lately since we're mostly using prefolds with the new little dude and they clean up easily. I think the hardness of your water would probably determine whether it helps or not.
I've never counted, but a box seems to last more than a few months here. I think even with the larger amount of detergent I am using now, the box I started at the end of September should last until at least mid February.
How do I know if I need to cut back on the detergent? Will there be bubbles if it's clean rinsing? I know I will have stinkies if I need more or less, but I would like to know before I have problems.
I see bubbles during the wash cycle but not during the rinse or second rinse. I think if you are slightly over then the second rinse will take care of it. There's no fragrance, so that may take some getting used to. Not sure if that helps.
Now that I have a calm moment, here's what I would do --
Try your wash routine with 1 scoop. Smell them. Anything? If yes, then wash again but only with 1/4-1/2 scoop, and hopefully that will take care of it. Then the next time you do a load, use 1~1/4 or 1~1/2 scoop, and see what happens. If your water is slightly hard, you might just need a slightly larger amount.
If you don't smell anything, go ahead and dry your diapers and put them on LO. Hopefully everything goes smoothly from there. If you smell ammonia coming off a wet diaper, you could try adjusting the detergent again, but I would also look at other aspects of your wash routine, which I don't remember right now. When I got ammonia off of wet (daytime) diapers, starting off with a warm quick wash and adding Calgon solved it. But your water and your machine are different from mine. I think you already know how to troubleshoot, so hopefully the different detergent will give you some different (hopefully better!) results.
Re: Tiny Bubbles
My current box is from an independent health food / pharmacy that was near my ILs place when we were visiting New England. You might try the store locator on Grovia's website to see if anyone local to you is carrying it. Or if a favorite online vendor has it, buy from them and build up some points.