[angzukofi]

[Chemistry/Math problem at end]
I've been making homemade HOCL(hypochlorous acid) and it doesn't last very long. I've been trying to find a way to prolong the shelf life, beside the obvious store in opaque PET container away from direct sunlight. (which by the way I have it in a spray bottle... I don't think the straw or sprayer mouth is PET, does that matter?)
One potential solution is adding phosphoric acid to act as a preservative and at the same time lowing the pH to my desired pH.
Another is adding hydrochloric acid to lower the pH and then adding a phosphate buffer like sodium phosphate to act as the preservative.

Now my question is, which solution would leave me with a cleaner or more stable product, and how much of each product do I need to add?

Say I have 6 liters of HOCL at a 6 pH
how much mL phosphoric acid do I need to add (and does it need to be 85% phosphoric acid?) To stabilize it at 5 pH. (explanation and formula would be greatly helpful for my future reference to calculate myself)

Now say I have 6 liters of HOCL at 5 pH (thanks to the hydrochloric acid) (from advice another told me that phosphoric acid does not mix well with hydrochloric acid and should not be added but instead a phosphate buffer) how much sodium phosphate should I add to have the same preservative effects of phosphoric acid (and does that affect the pH?)

Can I do add multiple preservative steps to prolong the shelf life more without tampering the HOCL pH and ppm ?

Does anyone know a better way to preserve the pH for up to 2 years?

[Hunter2]

Hydrochloric will destroy immediately to chlorine.
HOCl + HCl => H2O + Cl2
For cleaner it's better to have NaOCl not the acid.

[Borek]

Acidifying the solution is a sure way of speeding up the decomposition.

Buffers composition is typically calculated using Henderson-Hasselbalch equation, see examples here: https://www.chembuddy.com/buffers-composition-calculation