Forum Title: Wierd SLAM test results
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...
Category: pool Post By: Nick L (Tuscaloosa, AL), 03/04/2019

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?

- PEARL SCHWARTZ (Pittsburg, CA), 04/12/2019

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.

- MARIE MITCHELL (Kalamazoo, MI), 04/18/2019

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