SLAMing, water is clear but eating chlorine

[DagnyOH]

Hi all. I have been lurking and learning for about a month, and thought we were making great progress with the pool. Then we went on vacation, had to leave the pool on the chlorinator, and we're back at square one.

So here's the dilemma. Pre-vacation, we were scrubbing and shocking. Water was crystal clear, the clearest we've ever seen it. This is our 3rd summer in the house with the pool, previously used a pool service, and we figured out this can't be that hard. With the service water would often be cloudy between visits, and even when it was clear, it wasn't sparkling. By mid June we had the thing sparkling. It still wasn't stable - we were losing chlorine overnight, but pH, TA were stable. pH typically 7.2 or 7.8, TA a bit high around 150-180. CYA was high - initially reading 300, but we saw it dropping the longer the feeder was off and we get backflushing and replacing water in the pool. It was around 150 when we left. Hardness was around 100 and would occasionally add hardness rise to bring that up.

We come back from vacation, and we had lovely light green patches of algae on the bottom, chlorine was reading 0, although the water was relatively clear. So we go through several backflush, scrub, shock cycles, and we start to make progress. Algae is gone, chlorine is dropping overnight, but not as much as before. Seems like life is good.

We started wondering if our pool volume calculation was wrong, and even though we were shocking, because we had the wrong volume in the pool calculator, we were just nibbling around the edges and not really achieving shock level. I had estimated at 12,000 based on rough measurements, when we did more accurate measurements, we're actually closer to 20,000. To achieve shock level with our CYA, we were putting in about 360 oz of bleach, new calculation yields about 700 oz.

So in the evening, we scrub and skim and backflush and them dump in our 6 bottles of bleach. Our hardness was also really low, below 100, so we added calcium chloride to bring that up. The next morning we test the chemicals, expecting great things. Nothing. No chlorine. Zip, zilch, nada.

Urgh. We had 2 bottles of chlorine left, dumped those in the morning, which was consumed during the day. Then last night, based on the pool calculator, dumped in 6 more. Readings this morning look like they did yesterday

TH 250
FC 0
pH 7.2
TA 180
CYA 100

Any ideas on why our pool is consuming so much chlorine? Is it possible to actually overchlorinate and throw it out of whack, and did adding calcium chloride at the same time mess things up?

Thanks so much for any help you can provide. I have learned so much already.

 

[scott.MI]

Algae is gone, chlorine is dropping overnight, but not as much as before.

If your losing chlorine overnight, it's not completely gone. I don't know what your using to test your water with, but I think your biggest hold up it not having a test kit with the FAS-DPD chlorine test. Either get that test alone (26 plus shipping at tfttestkits) or buy a complete kit that has it included0) TF-100 or taylor K-2006. Ontop of that, read the the article on SLAMing. You need to maintain high FC levels until you pass 3 criteria...that's when the algae is gone completely.


If you have any lights or ladders...algae loves to hide behind the lights and on the bottom of the steps.

http://www.troublefreepool.com/content/125-slam-shock-level-and-maintain-shockingl

http://tftestkits.net/TF-100-Test-Kit-p4.html (entire test kit, includes FAS-DPD)

http://tftestkits.net/FAS-DPD-Chlorine-CC-s-test-p47.html (Stand along FAS-DPD chlorine test)

 

[PAGirl]

Ypu should be testing and adding more often so you don't fall below SLAM level at all.

 

[BoDarville]

Dittos to what scott.MI said. If your pool is still consuming chlorine, there is something organic still living in the pool. It could be algae hiding in and around ladders or lights, so it's worth taking a look at those. It could also be some other organic matter. Also, make sure there is not a dead critter in the skimmer basket (a long-shot, but it's happened before). Continue following the SLAM Process.

I'm also a little skeptical of the CYA level. Although backwashing and topping off with tap water will remove small amounts of CYA, I'm having trouble seeing how the CYA could go from 300 to 100 through backwashes alone unless you replaced about 2/3 of the water. If you are testing with strips, this could explain part of the issue. Most strips I've seen have broad ranges like "30-80", "over 100", etc. This is not precise enough to determine the maintenance and SLAM dosage of chlorine. I would suggest looking at the links in scott.MI's post. Having the proper test kit is the first (and necessary) step towards a Trouble Free Pool.

 

[DagnyOH]

Thanks for all the input. We bought the test kit, which arrived last week. The above readings are from the TF-100.

The CYA is a bit subjective as you all know. The 100 reading is coming from the kit as well as the aquacheck dip strips we were using previously. On the dip strips it used to read a bright purple, which was 300, now it's a rusty red which is in the middle . We know that's still high. On the pool calculator, I used 125 for the CYA to calculate shock level which comes out at 29. If I use 150 it generates 33, which would be 7 bottles of 8.5% chlorine instead of 6. We put 6 bottles in 2 evenings ago, 2 bottles yesterday morning (all we had left), 6 last night.

We pulled the ladder last month and found a lovely algae colony. It's still not back in the pool. Good thought on the light. We're pulling that this morning to see what is hiding there.

 

[scott.MI]

Did you get your 100 CYA reading by using the extended test method for testing CYA over 90?

http://www.troublefreepool.com/thre...Kit-Directions?p=203524&viewfull=1#post203524

 

[DagnyOH]

I did not. I used the directions that were with the test kit itself. Thanks for pointing me in that direction - will try the extended test and see what we get. Just cleaned the ooze out from the box behind the light. Not finding any other slimy stuff elsewhere.

 

[DagnyOH]

Progress! After getting the gunk from behind the light, chlorine stabilized. Finally! Did the extended test for CYA and came up with 150, so a bit higher than the test stick, but it appears to have come down. Haven't had to add any chlorine since last night. Thanks for all the advice. It is truly appreciated.

 

[Abigail K]

With CYA 150, we would advise a partial drain/refill to make your pool more manageable.

 

[DagnyOH]

With CYA 150, we would advise a partial drain/refill to make your pool more manageable.

We thought about it, and it probably would have spent less money on water than we did on Clorox! We're going to have to paint or resurface the bottom this fall as the paint has been failing for several years, so figured we would hold off until. We put it off last year as we didn't know which direction we wanted to go yet, and have been crawling around other threads on TFP trying to gather info.