How do you make the limpets only collect tritium fragments? Do you add everything else to the ignore list?
Short answer Yes
Its a case of knowing how to use the contacts panel properly.
First off when I said yes that is yes to metals and minerals, or mined commodities, Do Not turn off any of your raw materials, when a raw's bin is full the limpets will automatically stop collecting that particular raw, as soon as you use some they will automatically collect it again.
After you have fired a few seconds laser at a rock if you look in the contacts panel you can then ignore anything that you don't want to collect, the material will grey out and drop to the bottom of the list, if at a later date you want to re-activate that material you first have to find and fire at a rock that contains that material, it will then appear in the contacts panel greyed out you can then un-ignore it again.
Going back to the raw mats, If you keep an eye on them any bins that fill up easily and you don't really need can be traded at a mats trader.
Mining from a carrier as I do gives you certain advantages (storage space), it allows you to collect multiple materials and then choose when to sell them, it also allows you to mine easily out in the black (500+ly from civilisation) where every ring is pristine and no NPC's.