What if i had used BAC water but then separated a big vial into a few smaller ones and those small vials would maybe sit in the fridge for 3 or 4 weeks.
Even though it was BAC water would there be a big risk of bacteria forming because it sat there longer?
No. Once your compound is reconstituted with BAC, there's really no longer a concern about bacteria growing. BAC doesn't kill existing bacteria, however, it stops them from reproducing (that why it's Bacterio "static", ie, "standing still").
That remaining bacteria can, over time, degrade the peptide. Other factors will also break the peptide chain down over time as well. How long this takes depends on the stability of the peptide, temperature, exposure to light, excipients used (the peptide is only the size of a few grains of sand, the "filler" recipe is an important difference between UGL and Pharma), PH etc.
So TLDR there's no way to know how quickly it'll degrade. Some last for years in the refrigerator with less than 1% lost, others degrade significantly after 30 days.
What you can do is apply some rules to minimize degradation.
Dilute your compound to at least the same ratio as the pharma version is, or more, but never less. This can be established by looking at the packaging, FDA documents, or the clinical trials. IE, .5mg dose in .75ml water.
When dividing your reconstituted peptide into sterile vials (which will minimize introduction of bacteria from repeatedly piercing the same vial many times), use a .2 or .22ul uncharged PES syringe filter. This will sterilize the peptide, eliminating (almost) all remaining bacteria.
Practice disciplined vial hygiene. Always wipe top with alcohol swab and allow to dry.
Don't mix compounds.
Don't move your syringe from the compound vial back to the BAC vial for more water, which will contaminate the BAC vial with some peptide. Use another syringe, or just use a larger one to get all the water your require in one transfer.
Obviously keep as cold as possible, without freezing, out of light.
Minimize agitation of the vial (this was "disproven", but that was based on the wrong assumption of how that damaged peptides, and it DOES contribute to degradation, just not the way it was thought to). Don't store in a refridgerated drawer that will be moved back and forth, for example.
Pharma reconstituted Sema and Tirz last for TWO years in their pens, under refrigeration, using essentially the same ingredients we do. But that's done under perfect conditions, including radiation sterilizing the liquid after it's in sealed cartridges, ensuring a perfect PH, using container materials (unlike the garbage vials and stoppers we use) that doesn't contribute to degradation.