TX Torrential rains & my recent SLAM

[Jeffc2112]

Hi, so I just finished my first SLAM 2 weeks ago and enjoyed a clean clear pool with great numbers until the storms hit. Monday night we had torrential downpours overnight in Houston, between 6-10 inches fell, and I woke up to a Pre-SLAM looking pool, in just 12 hours! The numbers and picture are below, I'm curious, can that much rain bring down enough junk from the air to cause an algae bloom, or could it have been overflow from the surrounding ground running into the pool because it couldn't drain away quick enough? I'm thinking the latter, but have to ask...

Before the rain (monday at 7pm) , my numbers were:

pH 7.8
CYA 85
FC 8 (Target 9-10, added bleach to bring up to 12 overnight)
CC 0
CH 225
TA 100

After the rain, my FC reading on Tues morning was 9, probably due to dilution from the rain, but certainly high enough to keep algae away, right? Is there any way algae could bloom in 12 hours, or should I assume it was just runoff from the surrounding ground? I've added bleach to keep the FC at 12 or above since, and CC still is very near 0. I've seen my filter pressure raise 25%, 17 up to 21, so I know it's clearing the junk out, but I'm "shocked" at how nasty the pool looked in the morning after all the rain, check out this pic... Thanks for any help/guidance, Jeff

 

[smforte]

From the picture it looks as if you have a slope to your yard so I would assume run off. You need to SLAM..(maintain for your CYA LEVEL) ..If your pressure has risen 15-20% I'd backwash first before slamming. Your filter is catching the junk.

 

[pooldv]

I would bump up FC to 20 or 25 and run the filter 24x7 for a couple of days and see what happens. You could do an OCLT to see if there is additional chlorine demand.

 

[Patrick_B]

Your assumption is correct. One of the biggest misconceptions is that Rain destroys pool chemistry, when in fact it has little effect. Mind you, these are some heavy rains, but runoff is another issue. I can't tell how much runoff you might get from that picture, but what often happens to people is that they are on the very edge or already starting a bloom when they get a good rain. Judging by the picture, I would say this is a lot of run off because...look at the spa. It looks pretty nice from here.

In any case you ought to at least begin a SLAM. If you have to keep SLAMing, 85 Cya is really going to take a lot of Chlorine. As DV says, 20-25 but that will take a lot if you have to sustain that number, so if you are going to have to keep this going, you really want to bring that number down some.

 

[armsdealer]

Patrick, it doesn't rain in Midland...

 

[Jeffc2112]

I figured it out, somewhat. I suspect with 6-10 inches of rain, I probably did get some run off from the yard, but there's more. We had another big rain storm last weekend, and I noticed my yard and pool patio drains were slow to drain and I saw them back up back into the pool.

If you look at the pics, you'll see the dirty water draining back into the pool. The second pic is the yard drain, which I think is connected to the pool patio drains.

So, my next question is, could these drains be semi-clogged? Is it possible to drain those? I guess it's possible that they just can't keep up with the high amount of rain when we have big storms, but that seems unlikely, we get some big storms in Houston, I've gotta think they were made to keep up with the rain, and certainly not to drain BACK into the pool?

Anybody seen this before?

Thanks, Jeff