Pool green - do I need to SLAM it?

[hanesian]

Hi,

First year almost newbie here. Happy to say following the wisdom shared here, everything has gone very well all summer ... until the last few days, and my beautiful clear blue pool has turned green and murky. Based on my reading, I think I may need to do the SLAM process, but wanted to be sure and get a little reassurance since I'm still very new to this.

Here are my recent readings:

pH 7.5 (EDIT: 7.8 was a reading error)
FC 11
CC 0.5
TC 11.5
TA 120
CYA 30 (up from below 20 a day ago).

I think I neglected the stabilizer too long, and based on a CYA reading below 20 yesterday have added about 80 (EDIT, not 110) oz of stabilizer via socks in the skimmers. The CYA reading seems to be creeping up, but I understand I am not likely to see the results from that for another couple of days or so.

I added an extra bottle of bleach in the hopes that it might help improve the green murkiness in the meantime, and I can see my FC levels have increased from being low yesterday (was at about 3 ppm) to a bit high at 11 ppm.

From reading about the SLAM process it would seem I need to hit it hard with more bleach to get this under control, but I was looking for reassurance. I also need input on exactly how high to aim for the FC, since my CYA readings are so low, but presumably increasing based on the stabilizer already added. Should I shock it to 24 ppm and try to pass the tests there?

Thanks in advance for your help. Baby steps ...

 

[jblizzle]

You certainly need to go through the SLAM process. But, need to figure out your CYA first. That 110oz of stabilizer was pretty aggressive and may be more than we recommended. It should add 33ppm of CYA to the pool, but what did you start at? Had you never added anything with CYA in it so you were close to 0ppm or were you perhaps closer to 20ppm already?

I would suggest using a CYA of 40ppm to determine your FC SLAM level of 16ppm based on the chart. But, test the CYA again in a few 3-5 days.

Note, you should let the FC drop below 10ppm and then lower the pH to 7.2-7.4 before raising up to SLAM level again ... the pH test reads artificially high when FC > 10ppm.

 

[hanesian]

Thanks for your prompt response, Jason. I really appreciate it! :-D

I need to slow down and revise a couple readings I communicated in my first post. I was rushing out the door and wanted to get something posted.

First of all, my original CYA reading was below 20. I'm not sure how far below, or if it was zero, since the measuring tube basically only goes to 20, and the water was essentially clear so I was still seeing the black spot in the bottom of the test tube clearly. I had added some stabilizer earlier in the summer, but none for about the past 6 - 8 weeks. Presumably the CYA was well below 20, but not zero?

Second, I misstated how much stabilizer I added, as I converted from lbs to oz wrong. I added closer to 80 ounces, and the pool calculator indicated I should add 100 ounces. I simply ran out of the supply of stabilizer I had so stopped short of what I intended to add. Perhaps I misinterpreted the pool calculator results, but I don't think so. In any event, I've temporarily removed the stabilizer filled socks from the skimmers until we can clarify if I may have gotten too aggressive with that.

Finally, my pH reading is actually 7.5 not 7.8. I had taken several tests over the last day or so and just missed the pH reading from the most recent result.

Now for a few questions to clarify what you suggest, as I'm still confused. This is like learning a foreign language!

First, I have a SWG so my reading of the Chlorine/CYA Chart would seem to indicate a shock FC of 24, based on a CYA of 60. What do I aim at if my CYA is in flux, hopefully rising but last measurement at about 30 ppm?

Should I begin the SLAM process aiming for a FC of 24?

Thanks again!

 

[jblizzle]

Well, 80oz would have added 24ppm of CYA ... so if you were < 20 ... lets say 10ppm ... that would now put you around 35ppm ... so I would still say use 40ppm as the number to determine SLAM level. Put the sock back in because you want to be 30-40ppm for the SLAM process.

SLAM level is based on CYA level only ... you are 30-40ppm so use the SLAM level in the bleach chart (they are the same).

Like I said before I would aim for a SLAM level of 16ppm. Once you pass the 3 criteria to stop, then you should raise the CYA higher into the range for SWG pools.

 

[hanesian]

Gotcha. I understand now. Putting the sock back in and adding bleach to get FC up to 16 ppm to begin SLAM process.

Fortunately it's Saturday tomorrow so I'll have some time to devote to this. I'll be back with more questions soo, no doubt!

Thanks again.

 

[hanesian]

Well here's a quick update.

I began the SLAM process Friday evening, getting the FC up to the target of 16 ppm. Over the weekend I continued with testing about every 2 hours and adding more bleach as needed. Also scrubbed down the pool walls, etc. and kept the leaves and crud out as much as possible, and of course running the pump continuously.

Good news is the pool looks a thousand times better. Green color is almost gone, although it is still a bit cloudy looking in the deep end. Shallow end looks pretty clear, although not the typical crystal clear. Bad news is even though it's looking like its almost there, the FC readings continue dropping, especially overnight or after longer periods. Now for some readings.

The CYA has risen to just over 40 ppm and pH is steady at 7.5. CC is hanging in there consistently at 0.5 ppm. Here's a recap of some of the FC readings over the weekend.

Day 1
8:15 pm 16 ppm

Day 2
7:15 am 8.5 ppm - added 283 oz bleach
9 am 17.5
11 am 16
1 pm 16
4 pm 14. Added 75 oz
6 pm 14 added 90 oz
9 pm 18

Day 3
8 am 14, added 75 oz
10 am 16
Noon 14.5 added 57 oz
2 pm 13.5, added 94 oz
4 pm 14.5 Added 57 oz
7 pm 17
8 pm 17

Day 4
7 am 12.5, added 132 oz

Which brings us to present.

I hope the end is near, as work won't allow me to spend as much time during the day on this as the weekend affords. As I said, visually the pool looks WAY better than when I started. I'm just looking forward to the FC holding!

If I know I'll be away for a few hours does it help to intentionally get the FC higher than the target to allow for anticipated dropping, or does that not help?

Any comments or suggestions appreciated as always!

 

[Smykowski]

If I know I'll be away for a few hours does it help to intentionally get the FC higher than the target to allow for anticipated dropping, or does that not help?

I think that's a good idea. The good news is, you're making great progress so the FC drop looks like it has slowed down dramatically. If you're only going to be able to dose once in the morning, aiming a little higher in anticipation of the drop is ok. In your case, CYA of 40 shows a shock level of 16 and a mustard shock level of 24. I'd dose to 19 before you leave in the morning. This will get you high enough to allow for the days' drop yet stay above 16, but also keep you safely below mustard level to prevent any possible damage to your liner.

 

[hanesian]

Thanks for the help. I appreciate it!