SLAM... Can't get my chlorine levels up

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danlamar1

Member
Apr 26, 2024
14
Buckeye, AZ
So, I have been doing a poor job of maintaining my pool chlorine level and had an algae bloom. Trying to use the slam method to take care of it.

Starting chemistry:
FC 0
TC 0
PH 7.2
Hardness (500ish). Live in Phoenix with very hard water
Alkalinity 85
CYA 45

Pool is around 14000 gallons.
Using 12.5% chlorine, the calculator said 2 gallons should get to SLAM level of 16. I started dumping in chlorine and ran out at 14 gallons and never got a level higher than 3. The next night after work I dumped 16 gallons in and had a FC level of around 12 for maybe 20 minutes and by an hour all the chlorine was gone. Do I just need to keep adding more and more chlorine? For anybody that's been in this position, how much chlorine should I expect to use on this process? I don't mind shelling out the money if I know I'm gonna get there, but 30 gallons in 2 days and barely a blip of chlorine for a few minutes is a little disheartening!
 
I got the recommended test kit with the DPD fas... Don't remember the model number.

I just got the chlorine from my local pool store. It didn't smell very bleachy when I opened it, so maybe it's just bad liquid chlorine...I know it has a shelf life, but I'm both cases I used it the same day I bought it. Was thinking about trying bleach from home Depot...
 
Best place for liquid chlorine is Walmart. Or a HASA dealer if you have one near Buckeye.

Your chlorine consumption implies something like ammonia but your 0 CC and having a CYA level does not equate to that.
 
I used both test strips and the DPD test... Used the FAS DPD once it went over 5 that one time, and also used it intermittently to confirm. With the FAS DPD, I put 10 mL of pool water in and added a scoop of the powder. I'm the cases where the strips were saying no free chlorine, the solution also didn't turn pink. When it was reading chlorine it did turn pink. Then, added drops until it changed back to clear. Divide the number of drops by 2 to get FC... Results from that have always been consistent with strips also. Obviously, when I'm finally hitting higher levels it'll be more important for me to use the DPD test to get more accurate readings, but when I've got no measurable chlorine I don't want to waste all my reagents.
 

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High CC and no FC is ammonia. But your CYA would have to have been eaten up to create the ammonia.

Was the CYA much higher in the past?

You should consider draining this pool (be aware of risks draining above ground pools) and start over. The cost of water would have been far less than what you have spent on chlorine.
 
CC used to be FC that has interacted with 'stuff' in the pool. Its continued presence (high CC) indicates your pool has 'stuff' in it and increased chlorine is needed. CCs are created all the time but don't accumulate when there is adequate FC and sun exposure. Low or no CCs generally indicate either (1) adequate FC has been maintained over time or (2) no FC has been added recently (thus no FC to create CCs).

Combined Chlorine

Combined Chlorine is a generic chemical term for chemical compounds formed from the reactions of … Read more…
www.troublefreepool.com www.troublefreepool.com
 
Yeah, the CYA was higher about 6 weeks ago... Maybe about 80-90...I don't remember exactly, I was just surprised when I checked the CYA on Sunday and it was 45. I was planning to drain about half the pool before I started the SLAM, but then didn't think it needed it with the CYA level. I didn't know why it would've dropped.

I didn't anticipate spending this much on chlorine when I started this on Sunday... Do you really think it would be better to just replace a bunch of the water? Right now, the water looks great, I just know that it's temporary if I can't get the chlorine level up.
 
I'll definitely check a CC level tonight.

So, if I had organic matter that was chewing through the FC, it should be creating CC even if the FC was negative...so, if after adding 30 gallons of 12.5% chlorine in the past 2 days, if the CC is negligible, that would be an indication that the chlorine wasn't good. Am I reading that correctly?
 
If your CYA went down that much that quick, it is very likely you had a zero FC time period that allowed a bacteria to get into the water that consumes CYA. That creates ammonia. You should have eliminated that by now. So test CC and see what you get.
 
So, this morning when I didn't have any more chlorine, I put some pucks in just to try to keep some chlorine in the pool. I just tested and for free chlorine it only required 1 drop to go back to clear (<0.5 ppm of free chlorine). But...the CC test was 17 drops (8.5 ppm). So, I have relatively high CC and low FC. That would obviously indicate something in there chewing up the chlorine. Would 5 chlorine pucks do that just today? I assume not, so probably a result of all the chlorine I put in last night and the night before. Obviously, the TC on the "daily pH/chlorine" test was high.

So...is it possible that 30 gallons of chlorine in 2 days led to 8.5 ppm of CC without FC? I don't have enough experience to answer that question, but it seems like the CC should probably be some higher than that after that amount of chlorine... Was the chlorine a bad batch that was actually not as strong as 12.5%? I was frequently checking the chlorine level just a few minutes after dumping it in, and even in the same area that I dumped it in and it was frequently not registering any chlorine. I wish I would've been doing the DPD FAS so that I would've been able to see the CC change, but I wasn't so now I don't have that data. It was windy last night, but I stuck my nose down into one of the jugs to smell it because it seemed so un-bleach smelling, and I couldn't smell any chlorine.

All that being said...I have to do something so that I can get my pool in good shape...it looks good but I know it could bloom quick if I can't keep a decent chlorine level. Should I get some chlorine from Walmart and try adding that to try to SLAM it? Should I change the water? If there's concern about the quality of the chlorine, wouldn't I be better off just trying with different chlorine?

I really appreciate everybody's input today! Super helpful...and I'm learning a lot!
 
Post a picture of the date code on the chlorine bottle along with the label. Where did you buy it and how was it being stored in the store. In AZ it could be an issue, but HASA sources would know that...confusing.
 
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Here is the label. I didn't find a date code anywhere. It came in box that were 2 packs. It was stored inside the store next to the front door... As you would hope. Obviously, I have 29 more of those jugs... I did find a lot number on the box, but no date anywhere.
 
This is into the deep end, but we are all mystified. Something in your testing, or your chlorine is off. If you are game, try this:

To test the % of sodium hypochlorite in liquid chlorine:

Add 1mL of the LC to 100mL of distilled water.
Swirl to mix.
Add 1mL of the resulting mixture to 100mL of fresh distilled water.
Swirl to mix.
Use the DPD-FAS titration to get the resulting ppm’s of FC. The number of ppm’s is roughly equivalent to the bleach percentage.
Use distilled water only and do the test immediately. There’s no need to do extensive mixing.
 

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