Pool Over-Chlorinated (results =/= calculator)?

[mburn16]

Hello again all,

It seems my first-time-opening-the-pool-after-buying-it saga continues. I've repaired my tile, repaired the hole in my skimmer line, and filled the water up to the appropriate level. I've moved to the phase of adding the chemicals (SLAM, but also going to have to add CYA and MA)...but I'm not getting the FC/CC readings I feel like I should be getting.

Prior to yesterday, I had basically no FC in the pool and it was starting to develop a green tint, as well as getting increasingly cloudy. So, yesterday, after turning on the equipment, I added about 600 fluid ounces of bleach (8.25%), which the pool calculator told me should have raised the FC by (to) 11. Three tests prior to completing the water top off showed marginal CYA (<30), so I figured that should be sufficient. Took a reading last night about an hour after adding the chlorine, and the Taylor K-2006 showed it to be closer to 16! I assumed maybe the chlorine just hadn't circulated effectively yet, since I took the test water from the same wall as the return jets where I added the bleach, but this morning I had a very similar result and no CC....even though walking around the pool, I can smell the tell-tale chlorine smell that implies CC.

Hoping someone here can point out where I went wrong.

 

[drharris]

Are you confident in your pool volume?

 

[Patrick_B]

It just sounds like the pool is a little smaller than you thought, or perhaps there was an error in calculating/adding. It's only 5 PPM extra, and it will only help if you are Slamming to clear a pool. No worries, simply adjust down a little and see what happens on the next addition.

 

[JVTrain]

Two things at play here. First, your pool volume could be overestimated. Second, your test type is not the best for accuracy to determine higher levels of FC and any level of CC as accurately as the FAS-DPD chlorine test. DPD testing by color match is acceptable but not as fool proof. The K-1515 (A or C) that is included in the K-2006 Taylor kit and the TF-100 from tftestkits.net is far better for accurately determining FC and CC.

 

[mburn16]

I'm as confident as I'm able to be. The pool is 20'x40', with a 10' deep end, with the deeper parts of the pool taking up slightly less area than the shallower part.

20' x 40' x ~6' avg (best estimate) x 7.48 gpcf = 35900. The prior owner said it was a 35,000 pool, so I'm taking that as accurate and assuming that the average depth is actually a little less than 6'.

Actually the higher free chlorine levels are less baffling to me than the lack of CC, despite the condition of the pool pre-slam, lack of significant CYA amounts, and chlorine smell that is present when walking around the pool.

 

[mburn16]

Looks like I might have caused a little confusion. The test I use IS form the Taylor K-2006. It was the FAS-DPD, not a color match test.

 

[Richard320]

You won't always see CC with algae. Try Algae CC in the search box up above and you'll see that the subject comes up from time to time. Reading nothing on the test just means there's very little.

 

[Patrick_B]

Well, your higher than expected FC says otherwise. Nothing else explains it save perhaps test error, but I doubt that's it. No biggie, but try and calculate for smaller volume next time and see what happens.

 

[Fingaling]

Bleach is formulated to be the listed strength by the expiry date. If you have fresh bleach it is likely stronger than that concentration.

Don't worry about it with the bleach for now. If you're worried about your math you can check the math on solid chemicals much easier to figure out the volume.

 

[maverick1024]

did you do the 10ml or the 25ml DPD test? I originally did the 25ml and it took a lot of DPD powder to turn pink so when it finally did turn light pink it only took 2 drops to clear it up. This led me to believe my FC was really low and my CC was way high. The water is clear and i didn't smell any Chlorine so i redid the test using 10ml and got the opposite results showing normal FC and little CC.