Fully automated chemical dosing?

[Al762]

I've had my hot tub for about 10 months or so now. After the initial couple of months, the wife and I usually use it about once a week for about half an hour, so it's not a very heavy load.

On the first fill, I used the Frog@Ease floating system. It wasn't quite as "hands off" as the sales blurb would have you believe. There were a couple of occasions when the water turned green...

On the second fill, after a good flush, I used the frog spa floating bromine system. Shocking once a week with both MPS and a little granular chlorine shock. This has been mostly fine, but if I forget one week, it sometimes gets black mould on the cover, which i then scrub/jetwash off, and then supershock the water.

Now I'm looking at a more automated system. I have a home automation system doing a lot of stuff around the house, so why not manage my pool chemicals? After a bit of googling, I came across the raspipool project. This is a DIY project for swimming pools. It uses an ORP probe and a pH probe to measure the water, and automatically doses with bleach and acid to keep things balanced. Perfect for a forgetful person like me.

The thing is, the raspipool project uses liquid chemicals. These are more common for pools than hot tubs, where we tend to use solid pucks, or granules, for our chemical dosing. It's also a chlorine based system, and from what I've generally read, bromine is preferred in hot tubs as it's more stable at high temperatures, and doesn't gas off the same way as chlorine. (I assume this gassing off of chlorine will be degrading my hot tub cover.)

So - I guess my question is this:
I'm happy to do a first-fill balancing, but then would like to set something up to be as automated as possible. I'd prefer a bromine based system. I need to select *liquid* chemicals to pump into the hot tub. What are my best options to reduce my manual maintenance tasks as much as possible?

[turbulentwaters]

Thanks for sharing about the raspipool project. I'm also interested in automation and I had found a commercial option but have not used yet: https://www.hannainst.com/pool-line-ph-orp-controller-bl122-bl123.html. It's probably more difficult to make a clean installation of an automated system on a portable hot tub though due to space under the hood.

You should search this forum for "dichlor then bleach" method of sanitation and you'll get a lot more info on using liquid chlorine in hot tubs. I find it makes for very clean water and highly customizable for the bather load. You can initially dose your hot tub with NaBr ("bromine booster") at startup if you want to run "bromine". The bromide salt will be converted to active bromine upon addition of bleach or pool chlorine of any source. Ozone might obviate the need for going bromine since I believe nasty chloramines are burned away without shocking (pH must also be maintained in a stricter range with chlorine).

Also search for borax use. Helps buffer pH, maintain TA, and reduces the frequency of acid additions for me. It is tricky to prep though. Must mix in a bucket and then adjust pH to 7 using acid before putting in hot tub.