Dichlor/bleach Method Confusion

[Milly101]

I converted to the Dichlor/bleach Method and so far so good. After initial shock to 10 PPM, 24 hours later I was about 7.5PPM.

My question is , what PPM should i be keeping it at? Dealer instructions state to keep between 3-5 PPM at all times. So do I just add enough chlorine to keep it at 3-5 or do I add to keep it at 7.5 which seems to be my baseline.

Little confused.

[chem geek]

It looks like you are losing around 25% of the FC in 24 hours which is normal for a hot tub (the loss is slower at lower temperatures). So if you had 4 ppm FC, you'd end up with 3 ppm FC the next day which is fine. As for what FC level to target, that is up to you and you've really got two main choices. Most people don't want to nor like soaking in a lot of chlorine so they target a 1-2 ppm FC level just before their soak and they add enough chlorine after their soak such that they get 1-2 ppm FC for their next soak the next day or two (if longer than that between soaks, then you need to add chlorine more frequently in between soaks or get to a higher level after the soak so it will last longer). Though technically the FC probably drops to zero during a long soak with this approach, this is brief and the shock of chlorine right after the soak kills off any bacteria you may have shed. So while not acceptable in a commercial/public pool where person-to-person transmission of disease is something to prevent between strangers, this is far less of an issue in a residential spa where the main concern is preventing uncontrolled bacterial growth (and formation of biofilms). Bacteria double in population in roughly 15-60 minutes so don't get very far during a soak.

The other option is to target something higher such as 4 ppm FC which will probably last through your soak, but you will likely smell the chlorine reacting with bather waste (mostly producing monochloramine) in that case.

Just remember that without an ozonator and in a hot (104ºF) tub, every person-hour of soaking will need roughly 5 fluid ounces of 6% bleach to oxidize bather waste, though you really just add whatever is needed so you still reach your FC target for the start of your next soak.

[Milly101]

Thanx, that was a good explanation.