TECA skin serum · TECA scalp serum · malassezia-cautious hair oil
A funnel that fits a 24/410 neck (a kitchen funnel is too fat and will stop you bottling), 99% isopropyl alcohol for drying the beaker, and labels. Everything else you already own.
Splitting it across days costs you nothing in quality. The only price is extra beaker washes.
The oil goes first because it is the batch water would hurt most. It has no glycol, so a stray droplet sits in it as a separate blob where microbes could grow, with nothing to stop them. It gets the beaker straight off the shelf, bone dry.
The two serums need only a wipe between them. They are nearly the same formula. About 16 g of scalp serum clings to the beaker; tipped into a 650 g skin batch that shifts panthenol by 0.05% and everything else by less. Do the smaller batch first so the carryover lands in the bigger one.
One rule: if the beaker sits overnight, wash it rather than wiping it, even between the two serums. A wipe is only good enough back to back on the same day.
Label every bottle with the product, today's date, and ANHYDROUS — KEEP WATER OUT. Store cool, dark, and not in the bathroom.