Another chemical question

[spahopeful]

When is the best time to check Alk and Ph levels?  Also, is it Ok for chlorine to be at 0 8 hours after shocking or adding dichlor?

I get normal Alk and Ph readings 10 minutes after adding my 2 teaspoons of dichlor.  However, my Alk & PH are both very low 10 minutes after I shock with dichlor.  

[windsurfdog]

I only check pH once a week...normally after a morning soak.  This will give me an idea about how much, if any, soda ash may be necessary to add along with my shock (either dichlor or MPS, depending upon anticipated tub use that day).  So, to answer your question, I would check pH (TA if you want to...I don't check mine after the initial check behind a new fill) before you shock or add dichlor.  And, yes, not only is it ok but it is preferred to have chlorine levels down after 8 hours so I can soak in chem-free water next time!  And, IMO, once a week is all that is needed re: pH adjustments.  KISS...less is better.

[svspa]

spahopeful,

windsurfdog is right, you want to be able to soak with your FC level at or near zero.

My question though is you say it's down to zero 8 hours after a shock dose of dichlor, how much dichlor do you put in for your shock dose?

Normally a shock dose of dichlor will have a residual FC for quite a while, like over 5ppm for a day or more.

Sounds like your tub may have a high chlorine demand which implies something in the tub burning up the dichlor.

If you are religious about adding your daily dichlor dose and shocking with dichlor it seems to me your tub should have less chlorine demand, even getting some residual FC longer than 8 hours after your daily dose, let alone a shock dose.

Personally I would probably increase my dichlor dose for a while until I start getting residual FC for a longer time, just to feel comfortable that my tub is clean.

Remember there's a direct correlation between your free chlorine level and the potential for nasties to be in your tub. If you have residual FC you know nothing can be growing in your tub, when FC is at zero you don't know.

Steve

[spahopeful]

Steve,

Yes I am religious about adding 2 teaspoons of dichlor daily.  I normally shock with about 16 teaspoons of dichlor, but occasionally use MPS.   A month ago I was having problems with getting 0 FC levels just 15 minutes after daily dichlor so I refilled the tub and used SwirlAway.  I again had this problem a week ago and shocked with MPS and also 20 teaspoons of dichlor within a 24 hour period.  I was able to get the dichlor to read per my above post, but it is always back to 0 within 8 hours.  My water will get just a little cloudy after a week, but using something like Clean & Clear always gets it back to sparkling clean.  I am just concerned that my tub is not totally sanitary and don't know what else to do.  I'm looking for suggestions.

[hottubdan]

Chlorine is unstable in hot tub temperature water.  I would expect there to be a 0 reading 8 hours after adding.

That is why some people prefer bromine or baguanides.

However, with a backyard spa, with typical family use, dosing daily, will create safe water, I believe.

[tony]

Chlorine is unstable in hot tub temperature water.

Not entirely correct.  Sodium hypochlorite becomes unstable and begins to loose its effectiveness at 120 F.  At hot tub temps it works just as well as at pool temps.

[hottubdan]

Chlorine is unstable in hot tub temperature water.

Not entirely correct.  Sodium hypochlorite becomes unstable and begins to loose its effectiveness at 120 F.  At hot tub temps it works just as well as at pool temps.

I was referring to sodium dichlor.

[tony]

My mistake.  The same applies to sodium dichlor and all chlorines.  My interest in chlorine and disinfecting extends beyond hot tubs and into the food industry.  All chlorine is unstable and will dissipate over time...a relatively short time.

The following information courtesy of Ohio State University:

The effectiveness of chorine depends on the chlorine demand of the water, the concentration of the chlorine solution added, the time that the chlorine is in contact with the organism, and water quaility.  These effects can be summarized in the following manner:

As the concentration of the chlorine increases, the required contact time to disinfect decreases.

Chlorine is more effective as water temperature increases.

Chlorination is less effective as the water's pH increases (becomes more alkaline).

Clorination is less effective in cloudy (turbid) water.

When chlorine is added to the water supply, part of it combines with other chemicals in water (like iron, manganese, hydrogen sulfide, and ammonia) and is not available for disinfection.  The amount of chlorine that reacts with the other chemicals plus the amount required to achieve disinfection is the chlorine demand of the water.


From the FDA, chlorine starts to loose effectiveness at 120 F.  When chemically washing, you must not exceed 120, but should be minimum 113 F.  The range of 113 to 120 is where they say chlorine is most effective.

Many times you hear that bromine is better for hot tubs and chlorine is better for pools because chlorine is not as effective at hot tub temps.  I believe that this misinformation comes from the fact that chlorine does loose effectiveness at high temps, but much higher than what a hot tub will give you.  And according to OSU, chlorine in a hot tub is more effective than chlorine in a pool because of the warmer temp.  This is also backed up by the FDA.

[Vinny]

Steve,

Yes I am religious about adding 2 teaspoons of dichlor daily.  I normally shock with about 16 teaspoons of dichlor, but occasionally use MPS.   A month ago I was having problems with getting 0 FC levels just 15 minutes after daily dichlor so I refilled the tub and used SwirlAway.  I again had this problem a week ago and shocked with MPS and also 20 teaspoons of dichlor within a 24 hour period.  I was able to get the dichlor to read per my above post, but it is always back to 0 within 8 hours.  My water will get just a little cloudy after a week, but using something like Clean & Clear always gets it back to sparkling clean.  I am just concerned that my tub is not totally sanitary and don't know what else to do.  I'm looking for suggestions.

You do have a chlorine demand IMO. If your adding 20 teaspoons at 1 time you should have an incredably high chlorine level and it should last for days. I get a chlorine residue at times 24 hour later whith a starting value of 3 PPM.

Personally, I can't go more than 2 days before I get cloudy water. But even when my water is cloudy I have a 2 PPM residue the next morning with a starting value of 4 or 5 PPM.

Something is going on!

[svspa]

guys,

I can't speak for other people's tubs but 1 tablespoon of dichlor will yield residual FC in my tub for days if I am not soaking. For an example this week I haven't used my tub. 4 days ago I gave it about 1 tablespoon, last night I checked it and I was at about 0.5 ppm. I just checked it again and I am between 0.5 and 0 ppm. In about 16 hours I lost less than 0.5 ppm.

It would be interesting to hear from more of our friends here who shock with dichlor and how long after they shock they still have residual FC.

Seems like I remember Vermonter's FAQ also suggesting the downside to dichlor shocking is the long wait time for residual FC to get down below reasonable levels (like 5ppm).

Spahopeful, again my personal opinion is when your tub gets down to 0 shock it again, do this a few times and see if your residual starts lasting longer. You could also increase your daily dose. Personally I think this is one of those things where you'll eventually knock down whatever is burning up your FC and can then get back to a normal dose yielding residual FC for a longer time.

Vinny, I can't remember now, do you use MPS at all? You might try shocking with some MPS. That might oxidize out whatever is causing your cloudiness.
 
Steve

[Brookenstein]

I may have missed it, but what are you using to test your water?  I know when I super chlorinated with 3-4 TBS of dichlor couple months ago, my readings with test strips were suddenly off.  People wondered if I was bleaching out my strips.  One time I took the water to Leslies to be tested and there was I dunno .5 or 1 for a chlorine reading even though my strips showed 0.  That time I ended up dumping the water, but the next time it happened... I knew my water was ok, so I just ignored the readings and after a week or so, the readings were back to normal.  This seems to only happen to me, around the 3 month mark when I'm about ready for a water change.

[Vinny]

guys,


Vinny, I can't remember now, do you use MPS at all? You might try shocking with some MPS. That might oxidize out whatever is causing your cloudiness.
 
Steve

Yes I do and I didn't this time. It was bacteria I believe from not using the dichlor on a timely basis. If the water was new, I would have worked on clearing with dichlor, MPS and clarifier. Yesterday, it was still cloudy and I had the chlorine residue so I knew EVERYTHING was dead ... It was a beautiful day out so I dumped and refilled before the really cold weather hit. I'm hopefully all set until Feb/March!

I would chlorine nuke the tub, if it were my tub, it's amazing what a cup of dichlor will do! 8-)