After vacation green

[Dana0724]

So i went in vacation had perfect clear water. Before i left for 8 days my chemistry was as follows:

FC - 5
CC - 0
pH - 7.4
TA - 90
TH -160
CYA - 40?

I questioned i was reading CYA correct so i got a 50 standard and was going to test again when i got home.

Before i left i dumped a gallon of 6% bleach in and put a bunch of 3"pucks in my chlorinator. I know pucks aren't preferred but i just wanted to keep my FC up until i got back since i had no one to check on pool until i got back.

I got back yesterday and checked chemistry. Here are results

FC - 14
CC - 0
pH -7.4
TA - 90
TH - 150
CYA - 100

Before i checked CYA in my pool i used standard until i was confident i was getting 50 with the standard. I'm pretty confident it really is 100. My biggest problem though is the slight green tint.

My question is with the FC level so high how did i get algae? Also besides using pucks did i do anything wrong? Thanks in advance for your help

 

[Texas Splash]

I see two possible scenarios in what you are describing:
1 - Your CYA test results were still off and/or the CYA is so high the FC fell behind at some point. Seems odd now that you're showing an FC of 14, but earlier (before it shot-up) who knows?
2 - Could that green tint be from iron in the water, aggravated by the elevated FC level (very common) and not algae? If you've added enough well water since the fresh fill, the elevated FC could easily make the iron flare-up.

You might try doing an Overnight Chlorine Loss Test tonight. If you hold your FC by morning (ideally ruling out algae), you might consider letting the FC fall a bit to see if the green subsides confirming it was a reaction to the iron. I would also consider doing another CYA test because if it is indeed 100, you're in a tough spot. You might even have to do a diluted CYA test to make sure it's not much higher over 100. You can do the diluted test following the Pool School - CYA page starting at Step #8. Let us know how it goes.

 

[Dana0724]

Ok. I just redid the CYA test using diluted CYA test steps. Came out to 50 all 3 times I tried. So multiply by 2 and my CYA is really 100. I am confident now about my CYA. I think what happened was earlier before I got the CYA standard I added too much stabilizer and that is how it got that high. Other than draining and refilling my pool I guess I am stuck at that CYA

I started to SLAM earlier today based on 100 CYA(FC 39). I will continue SLAM until clear. I don't think it's iron only because my well water goes through a water softener and my hardness is 160 in the pool(0 from the hose). I am definitely no expert so maybe my iron is still up even though my hardness is not that high. Is there a way to check specifically for iron? Another reason I don't think it's iron is my FC was at 17(While I was SLAMing using 40 as a CYA) and the water cleared up beautifully once I got a new sand filter and used some clarifier to get all the white dead algae to sink to the bottom so I could vacuum them up

One thing I forgot to mention and may be the key but doesn't make sense to me. Since I started up my pool in late May until last week before I went I was running my pump 24/7. A day or two before I went on vacation I put in a timer and had the pump running 10 hours a day to save power but since all of my chemistry was spot on and the pool was crystal clear I thought 10 hours would be more than enough time. I always take my samples after the pump has been running for at least 30 mins so I get a good mixing of the pool water and get a true sample of the water. Could having the pump off for 14 hours allow FC to drop that much? My pump output is 75gpm max and my sand filter is an 18" sand filter so I assumed with that flow rate 10 hours should've been enough time.

 

[Texas Splash]

I don't think your reduced pump time had any impact. 10 hours is a lot of time. For checking iron, about the only way is to take a sample to the pool store. But I'd recommend grabbing a sample from the hose not the pool because the chlorinated water can influence the result. It may show something, but might not be perfect. But now that you have an understanding of what may have happened with the CYA and over-stabilizing, you are back in control.

 

[Sminor]

I doubt if it was your pump time as well. Most likely at the start of your vacation your FC was much lower than 14 for the first few days. The chlorinator might have kept up if your brought the pool up to slam level prior to leaving... But either way now your stuck with high CYA levels and a green pool. Good luck with the SLAM!!! Sounds like your already on top of it!

 

[Dana0724]

Well good news. It appears my pool has cleared up. Only took 2 or 3 days of SLAMing. My OCLT last night was 2 so I think tonight it will be 1 or less and my SLAM will be complete. Still frustrating to come home to a green pool but 2 or 3 days of hard work isn't bad all things considered. I just wish my CYA wasn't so high. Or it would be nice to be on city water so I wouldn't dry up my well replacing water trying to lower it back down. Oh well.