But from what I’ve seen, they’re all pretty much the same - Washing soda and an oxygen bleach (some brands add surfactants).
If you did it by approximate weight you’d be fine. But double dose probably wouldn’t make a difference either (the ingredients are easily dissolved).
I’d suspect the tablets contain a binder that might make them slower to dissolve.
If you want to get experimental, couch a spoon in one glass and a tablet in another and fill hald with hot water and see how long they take to dissolve.
I’m curious, but probably wouldn’t be curious enough to do it. I’d just Chuck in the scoop and give it a wash cycle and maybe an additional rinse (wash without powder) until the final rinse water from the clean cycle looks clear and tastes ok.
After a rinse or two I can’t imagine it’d be concentrated enough to case an issue from a tiny taste test (but I’m not a doctor, you do you).