Chlorine Levels: What is the normal dissipation rate?

Dear PoolForum,

I've been operating our tub since autumn 2011, and at first all was well.

I followed Jacuzzi Calgary's suggested chemical regime:

Add chlorine when levels get low through the week
Each weekend, add 'Foundation', 'Shock', 'Super Clarifier' and 'Secure'
Every other week, add 'Spa Perfect'.
Adjust for pH / TA as necessary.

The chlorine level would stay stable, going down slowly over a matter of days.

Then, they came and fitted a 'Clear-Ray' UV lamp, but removed my ozonator (I was out so I didn't see them do this).

Ever since, my chlorine just vanishes.
I get a reading of 0, I add 4 tablespoons of stabilised chlorine, and 24hrs later, it's at 0 again! (No use in between).

I eventually replaced the 'Clear-Ray' with a Delta UV lamp (much bigger and up to the job) and refitted a new ozonator.
(The back pressure of the Delta UV seems to be slowing down the ozonator water circuit, so I'm not sure if the venturi is sucking the ozone effectively. This is a separate potential problem I have yet to address).

However, I'm still experiencing the vanishing chlorine.

I've tried Super-chlorination, then Super-Super-chlorination (suggested by Jacuzzi Calgary), but even using a whole 2kg tub of chlorine made no difference!

Just how fast is chlorine meant to disappear in a normally-operating tub?

I've thought of switching to a salt-water chlorine generating system, so I'd never run out of chlorine, but if there's something wrong with my tub, then I feel I should identify it and get it fixed instead of adding another level of complexity that may not fix the issue.

What could be making my chlorine vanish so quickly?

Also, does adding chlorine lower pH?
I'm also fighting a low pH / high TA situation (see previous thread), and the chemicals used to raise pH ALSO raise TA, and I only know to lower both is via 'pH minus'!

Thus, all 3 readings on my water test strip are way off where they should be, every time I check!

(I read that aerating the water raises pH. Is that the same as running the seat jets with the air injection on?
I tried this and got higher pH [up c0.6], but higher TA too [up 10]!).

Any ideas would be greatly appreciated.
Thank you.

Jacuzzi J480 (2007) 1700 litres, ozonator, Delta UV lamp, 2 x Waterway 4HP main pumps, 1 x Aqua-Flow 1/15 HP circ pump, SmartSeal + Roxul skirting insulation, 100" x 100" Gator coverall

I don't know if anyone here can help as you have a hot tub, not a swimming pool. But at a guess I'd say you may want to drain your tub as it's only about 450 gallons and instead of throwing in all those fancy products with names that hide their ingredients, just use our BBB system that relies on a good test kit, and bleach, borax, baking soda, muriatic acid and stabilizer (CYA--Cyanuric Acid).

Hi Carl,

Not easy, as I can't source a good test kit up here in Canada, nor many of the suggested chemicals.
I very nearly couldn't find muriatic acid! Luckily, Rona carries it! (No-one else does!).

I can't monitor cyanuric acid levels, nor borate.
I only have test strips.

We also have very hard water here in Calgary, so not using 'Secure' (which I think helps address the damage hard water would otherwise do) is not yet a wise thing as far as I can see.

How does the BBB system address limiting the damage of very, very hard water..?