How Long Between Water Changes

[mlobitz]

I haven't refilled my spa since late October 2008. The water feels fine, no funny smells, PH and TA or within limits and the calcium hardness has held without a problem. I have cleaned my filters once a month by rinsing them in the dishwasher with baking soda. Is there some drop dead time I have to drain and refill my spa or can I just keep it going with proper maintenance.

I have a Hot Springs Grandee purchased in 2008.

[Nitro]

How many people have been using the spa, and how often?

What are you using to sanitize your tub?

[mlobitz]

How many people have been using the spa, and how often?

What are you using to sanitize your tub?

Good questions, I should have stated these already.

1-3 people

2-3 times a week max

silver ion insert

ozonator

2 tablespoons of dichlor weekly to shock

1 tablespoon of dichlor after each use

2 oz. of MPS before each use

[Nitro]

So we're talking 4 months. The fact that you're using Dichlor means your CYA has been increasing over those four months.

2 TBS = ~10ppm FC * 16 weeks = 160 ppm FC, which = ~140 ppm CYA

1 TBS * 2 per week = ~10 ppm FC * 16 weeks = 160 ppm FC, which = ~140 ppm CYA

That's ~280 ppm CYA, which is conservative. That's a lot!

I recommend draining your tub now. In the future, I'd recommend refilling at least every 2 months, with your bather load. Definitely not longer than 3 months.

[mlobitz]

So we're talking 4 months. The fact that you're using Dichlor means your CYA has been increasing over those four months.

2 TBS = ~10ppm FC * 16 weeks = 160 ppm FC, which = ~140 ppm CYA

1 TBS * 2 per week = ~10 ppm FC * 16 weeks = 160 ppm FC, which = ~140 ppm CYA

That's ~280 ppm CYA, which is conservative. That's a lot!

I recommend draining your tub now. In the future, I'd recommend refilling at least every 2 months, with your bather load. Definitely not longer than 3 months.

Thanks for the info. I'm set to drain and refill this weekend...just as an aside, what are the detrimental effects of high CYA in the tub? Long term exposure to people or general wear and tear on the tub?

[Nitro]

Thanks for the info. I'm set to drain and refill this weekend...just as an aside, what are the detrimental effects of high CYA in the tub? Long term exposure to people or general wear and tear on the tub?

Sorry, I should have mentioned that.

Cyanuric Acid (CYA) is a Chlorine Buffer/Stabilizer. If you don't have any in your tub Chlorine by itself is too strong, and can cause damage over time. This is the reason Dichlor contains CYA. However, if you have too much CYA in your tub, Chlorine becomes less effective.

HERE is a chart by Chem Geek that shows the relationship. From the chart you can see that Chlorine Effectiveness is a ratio of FC/CYA. As CYA increases Chlorine Effectiveness decreases, proportionally.

With your level of CYA (~300), you need 10 TIMES the amount of Chlorine to get the same sanitation effectiveness as I do with my CYA at 30ppm. My CYA stays at 30ppm, because I stop using Dichlor after a week or two and switch to bleach, which doesn't have CYA. If you want more info about this method, go HERE.

[Raegor]

Nitro... new tub owner here as well, another CYA question.

I understand your explanation of higher CYA means hgher chlorine demand and the need to add more chlorine to maintain.

I'm just wondering if there are any other issues of a high CYA, as far as health or tub damage. Meaning if we do maintain the chlorine demand is there any other concern?

Thanks.

[Nitro]

Nitro... new tub owner here as well, another CYA question.

I understand your explanation of higher CYA means hgher chlorine demand and the need to add more chlorine to maintain.

I'm just wondering if there are any other issues of a high CYA, as far as health or tub damage. Meaning if we do maintain the chlorine demand is there any other concern?

High Chlorine Demand (CD) is not the same as High CYA. CD is how much Chlorine the tub is using. High CD usually means there's a lot of stuff (bather waste) in the tub using it up. CD can be lowered by shocking. HERE is a post about that.

High CYA, on the other hand, means the same amount of Free Chlorine (FC) doesn't work as well. CYA cannot be lowered except by changing your water. I don't know of any other side effects of having high CYA, other than a reduction in Chlorine Effectiveness.

Chem Geek is the expert on CYA. Maybe he will weigh in also, or point to a post describing it in detail. This topic has been discussed a lot on this, and other forums. If you do a search for CYA and Chem Geek, you'll find a ton of info about it.

[EDIT]

I found an excellent post by Chem Geek that explains everything. Bleach In Hot Tubs.

[/EDIT]