Noob learning the hard way

[PaulR]

FPM gave you the one-line summary; if you're ready for it, let me try to unpack the situation in more detail.

If you haven't already read it, chem geek's main story is in this post. In summary, Richard had bacteria convert 20-30ppm CYA to ammonia, and it cost him around 60ppm FC to clear it up. (Many gallons of 10% and 12.5% liquid chlorine.)

That's a total of 18 jugs (3288 oz) of 6% bleach in one day.

1 gallon 6% bleach in an 18500 gallon pool is worth about 3.25ppm FC, so 3288oz or ballbark 25 gallons is worth about 80ppm FC, give or take. That would consume the ammonia produced from the conversion of CYA somewhere in the 30-40ppm range.

The problem is we don't know what your CYA was before this all started, so we don't know how much ammonia we're talking about. You are at around CYA 40 now, IIRC, but you were using the tabs and normally that leads to very high CYA concentrations. If we guess you were at CYA 100 before, then you need to contend with the ammonia produced by converting 60ppm CYA, and you are about 1/2 to 2/3 of the way done. If your CYA was higher than that previously, then you still have farther to go.

I know I would find that incredibly depressing! But, it's the best explanation we can come up with for the situation you are reporting to us.

I think you never got an ammonia test, is that right? If there's a pet store around that carries fish, it likely has an ammonia test. If there is still ammonia in the pool, you still have a ways to go on the bleach.

In these quantities it is really obviously worthwhile to shop around, see if pool stores or hardware stores carry liquid chlorine for cheaper than your bleach supplier. You figure the per-ounce-pure-hypochlorite price as
jug price / ( jug size x percentage )
so 6% bleach, 182oz@$2.94 is 2.94 / ( 182 x .06 ) = .269/oz
and 12% LC, 128oz@$4.40 is 4.40 / ( 128 x .12 ) = .275/oz
For these example prices it's pretty close and I'd go for the 12% just to have fewer jugs to carry around. That part is up to you.

--paulr

 

[chem geek]

(I wrote this as Paul posted his response above so there is some duplicate information here.)

The bacteria convert Cyanuric Acid (CYA) into ammonia rather quickly. You can read about my own experience with this here. There are only three ways to get rid of ammonia in pool water: 1) shocking with an oxidizer or 2) water replacement or 3) filtering it out with a zeolite (not sand, DE or cartridge) or similar filter (assuming it has enough capacity). The cheapest oxidizer available is chlorine and it is far less expensive than non-chlorine shock (MPS). Chlorinating liquid or bleach will add only chlorine to the water without anything extra that would affect water chemistry, such as Cyanuric Acid (CYA) from stabilized chlorine (Trichlor or Dichlor) or Calcium Hardness (CH) from Cal-Hypo.

The key to this problem is prevention. By never letting the chlorine get to zero (or nearly zero) one can prevent the bacterial growth that sometimes leads to this production of ammonia. If one is using only stabilized chlorine, then the CYA level can climb and algae can grow and consume the chlorine faster than it is released from the Trichlor tabs, hence leading to the bacterial growth and conversion of CYA into ammonia.

If you want some estimate of how much more chlorine it may take, you can get an inexpensive ammonia test kit from a pet/fish/aquarium store. The amount of chlorine that will be needed is at least 8 times that ammonia amount. However, an even better estimate can be made by doing a bucket test and scaling the amount of chlorine it takes before you get a consistent FC reading. 1/4 teaspoon of 6% bleach in 1 gallon of pool water is 20 ppm FC.

Richard

 

[PaulR]

However, an even better estimate can be made by doing a bucket test and scaling the amount of chlorine it takes before you get a consistent FC reading. 1/4 teaspoon of 6% bleach in 1 gallon of pool water is 20 ppm FC.

Thanks Richard, I'd forgotten about the bucket test!
--paulr

 

[b/o 402]

Did the bucket test today, twice. This does not look encouraging.
I had to add 3-1/2 tsp of 6% bleach to a gallon of pool water to get it to shock level. Any less registered the FC in the 5 ppm range.
The pool calculator says that would require 67 lbs of 65% Cal hypo - I can get 100 lbs for $300
or 660 lbs of 73% Cal Hypo - I can order 72lbs for $252
or 50 1 gallon jugs of 10% liquid chlorine for about $250 if I could find it
or 59 big jugs of 6% bleach ( about $155, assuming I could find that many to buy.)
Current FC <1.
Look, do I really have to kill these bacteria now? I really should have closed my pool by now. Aren't these bacteria going to die off over the winter anyway? Conversely, how worthwhile is it to get my pool chemistry perfect now, when I am likely to have to either do a water replacement or invest in a bunch of chemicals in the spring anyway?

 

[chem geek]

The bacteria are not really the problem anymore -- they've already done their damage by converting much of the CYA into ammonia. The chlorine doesn't "feed" the bacteria -- it only kills them -- but the chlorine does combine very quickly (in minutes) with ammonia to form Combined Chlorine (CC) and that's what seems like "feeding" or an insatiable appetite in the pool.

So with lots of ammonia in your pool water, adding chlorine would quickly get converted to CC. You shouldn't be measuring any significant Free Chlorine (FC) shortly after adding the chlorine to your pool water (including that in the bucket). So I am confused by your readings of "in the 5 ppm range" at least until you got to a point where you converted all the ammonia to CC. After that point, it takes around half that CC amount as additional chlorine to get rid of it and you would then measure lots of both FC and CC.

Just to make absolutely sure, I think you should really get an inexpensive ammonia test kit from a fish/pet/aquarium store. It should read off the charts if your bucket test was accurate, even if you were to dilute your sample significantly.

If I assume that your bucket test was correct, then yes, you could just let your pool go and dilute the water for closing. Upon opening, you'll probably need to replace a lot of the water as that should be less expensive than trying to get rid of the ammonia through oxidation (by chlorine or any other oxidizer). You might also have algae at that time, but since the water is already getting cold, it hopefully won't be too much if you don't wait too long to open the pool in spring (i.e. take care of the problem before the water warms up to much).

Richard

 

[b/o 402]

yes, you could just let your pool go and dilute the water for closing. Upon opening, you'll probably need to replace a lot of the water as that should be less expensive than trying to get rid of the ammonia through oxidation (by chlorine or any other oxidizer). You might also have algae at that time, but since the water is already getting cold, it hopefully won't be too much if you don't wait too long to open the pool in spring (i.e. take care of the problem before the water warms up to much).

Richard

Thanks, Richard. I was hoping you'd say that.
Can you explain what you meant by "dilute the water for closing?"
How much do I need to dilute it now, and what percentage will I need to replace in the spring?
Thanks!

 

[chem geek]

It's up to you, but I figured you were probably going to lower the water level for winter closing so when that gets filled back up early spring that will be some partial dilution already. If you wanted to do multiple partial drain/refills now, that would be fine -- again, it's up to you since it sounds like there is still a lot of ammonia left to go (please get an ammonia test kit to be sure). As for how much it's going to take -- it's a lot if you want to significantly reduce the amount of chlorine that will be needed to clear the pool of ammonia upon spring opening. Diluting by half will cut down the amount of chlorine needed by half, etc.

I'm not sure if PolyQuat 60 will be an effective algaecide with all of the ammonia in the water, but it's something you could try. Note that the product is viscous and requires thorough mixing, usually by running the pump for 24 hours after adding the product so would need to be done before you close and lower the water level (unless you are able to circulate without use of the skimmer and only with floor drains).

Unfortunately, letting your pool go over the winter right now could result in even more ammonia since there is still CYA left in the pool from your last measurement. If it were my pool, I'd tackle the problem now and keep the pool sanitized over the winter, but then I don't live in a freezing climate so I maintain chlorine levels during the winter which is harder to do if the pool freezes over. It really is up to you.

 

[polyvue]

Can you explain what you meant by "dilute the water for closing?"
How much do I need to dilute it now, and what percentage will I need to replace in the spring?

Richard answered your question, but I just wanted to say that although this has been a frustrating and thus far inconclusive process for you, no one will think less of you for wanting to put this task off for the winter. If this was my pool, after the bucket test analysis I would have decided on a 100% drain and fill, but I realize that water is not cheap in every part of the country. Good luck to you on the close. At least you now know what it will take to get your pool ready for the spring!

 

[frustratedpoolmom]

Good luck with whatever you decide - and I'm sorry you had to learn the hard way about Ammonia.