Wierd SLAM test results

[SamirP]

This is the first time opening a pool for me, and first SLAM. We've got an 18000 gallon AGP. Since we're in Austin, TX and it doesn't really ever freeze (much) here, I had left the pump and all the plumbing hooked up and just put a cover on the pool. We just have a regular sand filter (no DE or anything). And I'm using the TF-100 testkit.

So, taking the cover off, the water looked cloudy, but blue. But I could see a bunch of green algae in the basket under the window on the pump. The water temp is in the low 70's.

Initial test levels were:
FC - 0
CC - 0
TC - 0
TA - 120-130?
CYA - 30-ish
Ph - 7.8

There's not a test for borates, but we had added enough borax last season to get to 50 for borates.

My goal FC for a SLAM is 12 (according to poolmath). That night I added 288 oz (3 of the 96 oz jugs) of store-brand bleach. I didn't retest that night or the next morning to see what the chlorine level got to after adding bleach. I figured stuff was going to be off anyway, and the first day wouldn't really matter much.

The next evening (yesterday), initial testing showed around 3ppm FC (0 ppm CC). I added another 3 jugs (288 oz) of bleach, and tested again around half an hour later, and only got FC=5ppm/CC=0ppm. Weird. I added my last three jugs of bleach, tested again around 30 minutes later and now FC=7.5 ppm, CC=0ppm. I was out of bleach at that point and had to admit defeat for the night.

This morning, I retested, and FC held around 7.5 ppm and CC was still 0. The green crud in my pump seems to be fading, but its still green-ish in there.

So, it seems to take a lot more chlorine to raise my FC that I thought. Last year I could reliably raise the TC by 4 or 5 ppm with around a gallon of bleach.

I maybe got a batch of really old bleach from the store (possible), or I'm not doing the tests right, or I've massively misjudged how much CYA I have in the pool (we ended last season at 60 for CYA). Is there something else that could be going on? I'm using last year's test reagents, maybe that's not helping?

The pressure on my filter has gone way up as well. It used to run at around 20 psi last season, but now its running around 40psi. I backwashed for 3 or 4 minutes, and then rinsed for a minute, but it didn't make a dent in the pressure. Its still running at 40 psi. Am I doing that right? Its how the manual for the sand filter said to do it. I've only been running the pump for a few hours at a time because I'm not sure if its okay to run it continuously at that high of a pressure.

Any idea on what's going on here? Yikes...

 

[JohnT]

What you probably were seeing is the rapid consumption of chlorine by biological contaminants like algae.

The first day of a SLAM matters a lot, because that is when the chlorine consumption is highest. Sometimes it will all be gone in an hour.

I'd bet your gauge is shot. Does it go to zero when the pump is off? Is flow from the return good?

 

[SamirP]

Crud...I knew better, but slacked off anyway. Ugh...

My understanding is that chlorine consumption would show up in the CC number? Or is that for non-algae consumption?

The return flow from the pump is pretty good. Visually it looks as strong as it ever was. I'll check to see if the gauge goes back to zero when we turn it off.

 

[SamirP]

Yup...gauge is shot. Turned off the pump and it went down to 30psi. Turned it back on at went back to 40psi. I'll go ahead and keep the pump running 24/7 until the SLAM is over.

I'm about to go get more bleach, and be a lot more diligent about testing. And at this point I'm assuming the low numbers are because of rapid consumption.

Thanks for the help!!

 

[madwil]

Algae or other organically can cause cc but not always. If enough fc is added to sanitize it can clear cc as quick as it is generated it just sucks down your fc. My worst outbreak, which lead to my discovery of tfp, my cc never got over 1

 

[kimkats]

The next thing to do is to take a picture looking down at the steps. That will show you the progress your hard work is making. Your eyes will not see it day to day. The pictures will tell the story.

You are on the right track. Just hit it harder and you will win!

Kim

 

[SamirP]

Thanks for the help, everyone!! I think I'm done SLAM-ing, but now I'm not sure. After my initial additions of several jugs of bleach ended up not moving the needle much, I got into a mode of just adding bleach by the gallon jugs, and so I ran with FC that was generally higher than the target of 12 to 16 (depending on my CYA result of 30 to 40, depending on the day...I suck at CYA testing still).

Here are my test results for the last several days. Can you all look it over and make sure I didn't miss any steps and am really done?

Date	Morning FC	Morning CC	Evening FC	Evening CC	Overnight loss	Notes
3/15	9	0	25	0		Added 3 gallons bleach before evening test
3/16	22	0	18	0	3
3/17	16	0	14	0	2	Added 1 gallon of bleach before evening test, lots of daytime FC loss
3/18	12.5	.5	19	0	1.5	Added 3 gallons of bleach before evening test
3/19	21	0	-	-	-2	Gained 2 ppm overnight? Called it a finished SLAM
3/20				14	0

Not sure if the last couple days make sense, but with the test results on 3/19 I declared it finished and finally stopped the pool pump and didn't test again until the next evening (3/20). On the next day's test, I had 7 ppm of FC loss in roughly 24 hours.

So now I'm doubting myself and I'm not sure if my SLAM was really over, or if I just had a weird reading. The night before the last day had only a loss of 1.5, so I was pretty sure I was close to finished based on just that.

I'm in Austin, Texas, and was really sunny today and the water temp has crept up to 78 or 80 degrees. It might be actual honest FC loss. If the SLAM is really over, I need to get my CYA up a bit so I don't run through as much bleach. Last year I got some advice from someone on here to run CYA at 60 and that really helped with not running through so many chemicals, so I want to do that again this year, but only after I'm sure things are stable.

 

[duraleigh]

What does your water look like? Why do you think you gained 2 ppm of FC?

 

[SamirP]

The water looks crystal clear, beautiful even. We have a lot of pollen flying around right now, so I need to skim off a bunch of new crud on the water every evening to get it looking that way again. But after skimming it looks great!

Looking back, I think I messed up the testing on either the night before or the morning after. I'm colorblind, so its sometimes hard to decide when the water in the test cylinder has gone clear and when its still slightly pink. I get my kids to help with it, but I suspect each kid has a different threshold for "clear".

This morning I took another reading and it was 7ppm/0ppm, so a loss of 7 overnight (with the pump off). I guess I'm not done with the SLAM. The water looks so good, though. I added enough bleach to get back over 16ppm and kicked the pump back on.

- - - Updated - - -

Also, is running with FC too high a bad thing? Wasteful of chemicals? Other downsides?

Should I be trying to keep it closer to 16 ppm, instead of in the 20's like I've been doing? I figure if I've got some head room for FC drop, it won't dip below the SLAM level, but I could be wrong on that.

 

[SamirP]

Last night's test was FC 18/CC 0. This morning it was FC 16.5, CC 1.5.

The SLAM goes on.

 

[duraleigh]

Last night's test was FC 18/CC 0. This morning it was FC 16.5, CC 1.5.

The SLAM goes on.

I'll bet you pass very soon....probably tonight. Keep your FC up to shock value all day.

Remember on the FC test that the test is complete when the LAST drop you add, results in no further change to the sample. Subtract that last drop and the result is your FC. (I think you may have done the test a little inaccurately to get that 2 ppm increase)

You are doing great.....keep at it.

 

[SamirP]

Aaaand...I'm done!!

Last night's test was FC 19/CC 0, and this morning's was FC 19/CC 0.

Whew...only took around 8 days. Thanks for all the help!!!

 

[madwil]

Congrats!

 

[duraleigh]