I Think My Approach To This Is All Wrong

[chem geek]

You aren't in immediate risk so long as you're able to register some chlorine in the tub and start your soak with at least a little chlorine. The biofilm is mostly annoying as it creates a larger-than-normal chlorine demand so ends up costing more. There is the very small risk of some chunk of it dislodging and not breaking up (if it broke up the bacteria within would get killed fairly quickly) and that chunk somehow getting aerosolized, you breathe it in, and it overwhelms your immune system. Pretty unlikely. On a spa forum where I kept track of all kinds of hot tub itch/rash/lung incidents and one Legionnaires' Disease incident they were all due to too low a chlorine level for an extended period of time or to use of some "alternative" sanitation systems or for some itch/rash incidents using Dichlor-only for too long.

Yes, I live in that San Rafael in Marin County. The sub-station I know about is near downtown on 2nd street and from what I gather there used to be a slot car track on 4th street so that may be the area you are referring to (the other slot car track was apparently in the Woodland area, but I don't think there's a sub-station there).

 

[Bimmer]

You aren't in immediate risk so long as you're able to register some chlorine in the tub and start your soak with at least a little chlorine. The biofilm is mostly annoying as it creates a larger-than-normal chlorine demand so ends up costing more. There is the very small risk of some chunk of it dislodging and not breaking up (in which case the bacteria within would get killed fairly quickly) and that chunk somehow getting aerosolized, you breathe it in, and it overwhelms your immune system. Pretty unlikely. On a spa forum where I kept track of all kinds of hot tub itch/rash/lung incidents and one Legionnaires' Disease incident they were all due to too low a chlorine level for an extended period of time or to use of some "alternative" sanitation systems or for some itch/rash incidents using Dichlor-only for too long.

Yes, I live in that San Rafael in Marin County. The sub-station I know about is near downtown on 2nd street and from what I gather there used to be a slot car track on 4th street so that may be the area you are referring to (the other slot car track was apparently in the Woodland area, but I don't think there's a sub-station there).

 

[Bimmer]

Well since I started slowly adding chlorine, the water has gotten and is staying crystal clear. I'm averaging about a cup of chlorine a day since we use it everyday. Will let you know when I get the drop test kit and Dichlor.

 

[mx702]

Just as a heads up to help you with The Pool Calculator, I believe you are grossly overstimating your volume. Judging from the pic your tub looks no where near 650 gallons. I have one of the largest available (92" x 92", 7 seater with no lounger) and mine only holds 400. Doesnt appears to be very deep, either. Im guessing closer to 300.

 

[Bimmer]

Just as a heads up to help you with The Pool Calculator, I believe you are grossly overstimating your volume. Judging from the pic your tub looks no where near 650 gallons. I have one of the largest available (92" x 92", 7 seater with no lounger) and mine only holds 400. Doesnt appears to be very deep, either. Im guessing closer to 300.

I'll post measurements tomorrow. Thanks!

 

[Bimmer]

Just as a heads up to help you with The Pool Calculator, I believe you are grossly overstimating your volume. Judging from the pic your tub looks no where near 650 gallons. I have one of the largest available (92" x 92", 7 seater with no lounger) and mine only holds 400. Doesnt appears to be very deep, either. Im guessing closer to 300.

I'll post measurements tomorrow. Thanks!

Ok, you were right. The quote I had was almost double. I figured it before I found the pool calculator.
The square mass of the spa measures approximately 67" X 66". That doesn't figure in the small portions that extend say beyond the filter housing and the smaller portion on the end closest to the deck. The seating area fluctuates as it is not flat. It has curves and therefore varies especially the one corner near the steps (opposite end from the deck) where the seat drops nearly to the bottom of the spa. This being said, the first level is 16" from the top and the bottom of the spa is 28 inches from the top. Roughly I think that gives me a figure of around 370 gallons.

Obviously, this means that I have been over-adding the chemicals I've been using. Still no sign of problems though. The spa still looks and smells as it should. Crystal clear with a smell of a little chlorine but nothing overpowering or offensive. I certainly have not had an eye burning from the water or anything like that, but again, because of the 100 degree temps I've been adding cold water to bring the temp down so that it is more refreshing.

 

[mx702]

It's not going to make a huge difference, but I'd say your estimation is still over by 100 gallons. Remember, you do not fill the spa to the very top with water. IMO...trying to calculate the volume of a spa using mathematics/formulas isn't really practical due to all the odd shapes and contours. Looking online at spas that state it's capacity with similar dimensions and seating configurations would be more accurate. Better yet, next time you fill take a before and after reading on your water meter.

Enjoy yout tub!

 

[Bimmer]

We just got back from Lowe's with some Swimmer's Choice Granular Shock. I know what you're going to say about shock but hear me out a moment. They only had 25# tubs of Dichlor for like $80. I got to looking at the Granular Shock and the labels were exact duplicates, to the letter. The ingredients were exactly the same with exactly the same percentage of those ingredients. The instructions for use were exactly the same so I bought the $5 box for around $18 as opposed to almost $4 for a single #1 bag.

It has:
Sodium Dichloroisocyanurate dihydrate.....99%
Other Ingredients ................................... 1%
Total ...................................................... 100%

Available Chlorine .................................. 56%

Yesterday I drained the spa down to just above the upper jet and then topped it off and added bleach. Is it a no-no to add this Granular Shock (Dichlor) while there is any bleach in the water?

Thanks!

 

[chem geek]

It's Dichlor like any other Dichlor. You use it after a fresh refill as your regular chlorine source until your CYA reaches about 30 ppm or so. Then you switch to using bleach after that (maybe using Dichlor for one day per month to build up the CYA that slowly gets broken down). You do NOT use bleach initially after a refill (except for decontamination if you are doing that) since it is too strong without any CYA in the water. After you've already reached 30 ppm or so, if you use this Dichlor that you've bought the active chlorine level will drop over time (assuming you maintain the same FC level) and the water will turn dull/cloudy sooner than it would if you were to use bleach. You also increase the risk of getting hot tub itch/rash over time as the chlorine gets weaker and weaker due to the CYA buildup.

Remember that for every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm.

 

[Bimmer]

This "Swimmer's Choice Granular Shock" says 9oz. treats 10,000 gallons. That means 1oz treats 1,111 gallons. So for an approximately 350 gallon spa I'm using about 1/3oz or 2 teaspoons. Does this math sounds accurate to you?

 

[chem geek]

You can use The Pool Calculator setting Size to 350 gallons and then under Effects of Adding Chemicals where it tells you that 2 teaspoons (2/6 or 0.33 ounce) raises the FC by 3.9 ppm so about 4 ppm. You can also use the upper part "FC" section, but it doesn't give enough decimal places. You can multiply your FC difference by 10 to get more accuracy (so 0 to 40 ppm shows 3.4 ounces weight, 3.2 ounces volume, and holding your cursor over that shows 3 ounces 1 teaspoon so 19 teaspoons which dividing by 10 gives you 1.9 or roughly 2 teaspoons).

 

[Bimmer]

Thanks Chem Geek! How long should I wait to use the spa after introducting the Dichlor? I don't intend on using the heater as the temps here are hot and cool spa feels refreshing. I have been running the jets periodically just to get the Dichlor distributed.

When I saw that I was only going to be using 2 teaspoons to start and then bleach to maintain, I took the 5# box back to Lowe's and got a single 1# bag.

 

[chem geek]

It takes more than 2 teaspoons to build up enough CYA, so I presume you mean that you already had CYA in the water from earlier Dichlor, right? When starting from a fresh refill, it usually takes a week or so of use to build up the CYA level. 33 ppm FC of cumulative Dichlor would be 30 ppm CYA.

With either Dichlor or bleach, you can enter the spa when it's thoroughly mixed which with a spa and good circulation is only 10 minutes or so. However, most people add the chlorine AFTER their soak so that they start their soak with 1-2 ppm FC so that they don't notice the chlorine during their soak. If you are soaking with non-family members and are afraid of person-to-person transmission of disease, then you can dose some before a soak (up to you).

 

[Bimmer]

It takes more than 2 teaspoons to build up enough CYA, so I presume you mean that you already had CYA in the water from earlier Dichlor, right? When starting from a fresh refill, it usually takes a week or so of use to build up the CYA level. 33 ppm FC of cumulative Dichlor would be 30 ppm CYA.

With either Dichlor or bleach, you can enter the spa when it's thoroughly mixed which with a spa and good circulation is only 10 minutes or so. However, most people add the chlorine AFTER their soak so that they start their soak with 1-2 ppm FC so that they don't notice the chlorine during their soak. If you are soaking with non-family members and are afraid of person-to-person transmission of disease, then you can dose some before a soak (up to you).

I don't have a test kit yet to give you levels on CYA. I emptied all but about 5 gallons of water so we're starting from scratch again. For now it's been pretty much just my wife and I using the spa. This is the first time I've used Dichlor at all. Previously we were just using bleach on average about a cup a day considering we were using the tub about twice daily.

 

[chem geek]

Oh, well if you are starting with a mostly fresh refill, just use Dichlor only until you've cumulatively added around 33 ppm FC. Since 2 teaspoons is roughly 4 ppm FC in your spa, that means about 8 doses so about a week if you use the spa every day (longer if you use it less). Don't switch to using bleach until after you've added this amount of CYA via the Dichlor. Otherwise, the chlorine will be too strong for too long.