After 11 yrs of IG pool ownership, I have finally broken down and purchased a new tub. I have the 500 HotSprings Grandee http://www.hotspring.com/Spa_Showroom_Hot_Tub/spa_model_grandee.html coming next week. I plan on running chlorine. My main question is whether I should purchase some diclor or just continue to use CYA/bleach?

Here are my numbers that I will fill from:

pH= 8.2
FC=0.5
TA=50
CH=110

HotSprings recommends (in this order) balancing the TA to 80 ppm. Then, they recommend balancing the CH to 100 ppm. I am good here for now. Then, they target the pH for 7.4 to 7.6. I will use HCl unless there is a reason not to use this product. They do suggest using either NaHCO3 (to raise) or NaHSO4 (to lower) but I always have HCl on hands.

Finally, the manual says to add 3 teaspoons of diclor and bring the water to temp and run all of the jets. If the FC is at least 3 ppm then I am done. If there is less than 3 ppm FC, redose with 3 teaspoons of diclor until the FC holds above 3 and repeat as necessary.

The recommended levels are:
TA=40 to 120 ppm
CH=100-150 ppm
pH=7.4 to 7.6
FC=3-5 ppm

CYA is not mentioned. I will also add borates to 50 ppm as I enjoy the water conditioning benefits. Any other ideas?

Have you looked at How do I use Chlorine in my Spa (or pool)? basically, the idea is to use dichlor until you have CYA at 20-30ppm, then switch to bleach. You won't need to change the water as often. Of course you can also just add straight CYA to get to 20-30ppm and use bleach from the start.

Managing pH in a tub usually requires pretty small quantities (teaspoons) of acid, so most people find it easier to use granular "dry acid" (sodium bisulfate) often sold as "pH Down" in the pool store.
--paulr

I have read that thread...my concern with dichlor is that 1 oz only gets my 500 gal tub to 7.6 ppm of CYA. 4 oz with get CYA to 30 but is also adding 33 ppm of FC. It would probably take a month to need that much diclor. And along the way, CYA is low. Is CYA less of a concern because the tub is covered the majority of the time?

It would seem simpler (to my inexperienced tub users mind) to just start with CYA/bleach. Maybe I am missing something? I must be because it seems that so many use dichlor in tubs.

You are correct that Dichlor-only users experience higher-than-normal active chlorine levels during the first days after a fresh refill. This isn't a disaster, but it's true that the active chlorine level is higher. The recommendation in the manual to start out with 3 teaspoons of Dichlor for the 500 gallon tub would add about 4.2 ppm FC and 3.8 ppm CYA to the tub. The active chlorine level that results at lower temps (more like a pool) would be equivalent to around 1.8 ppm FC with no CYA so not much different than many commercial/public indoor pools. At hot spa temps, it's more like 2.2 ppm FC with no CYA.

It sounds like the plan is just for one person soaking for 20 minutes since that would require just a little more than 1 teaspoon of Dichlor to oxidize bather waste. So yes you are right that it will take around 20 such soaks before the CYA were to build up to 30 ppm. And yes, this is what Dichlor-only users live with -- inconsistent active chlorine levels that are high at the beginning and then too low months later which makes them have to change the water sooner.

So you can certainly start out by adding 30 ppm CYA initially and then use bleach and skip the Dichlor entirely. That is the technically better approach. The only reason it's not described in the Using Chlorine In a Spa article is that the CYA takes a while to dissolve so is less convenient that fast-dissolving Dichlor. Also, many people do some form of initial shocking and can use Dichlor to do so -- say, going to 10 ppm FC so getting 9 ppm CYA right away.

The key is knowing what happens and making your own choices. If you add CYA at first, let us know how quickly it dissolves (you can put it in a sock or panty hose to monitor it's progress of dissolving). I would think that it would dissolve more quickly in the hotter water, but one never knows.