Hello, Everyone.

I've owned a 24' above ground vinyl pool, 13,500 gallon (15k gallon according to the salesman), going on 5 years now. When it was originally installed, it came with the Nature2 system. During the first year, I thought it was the greatest thing in the world. Each subsequent year, I constantly fought algae problems. This year, I've decided to dump the Nature2 system and go with the BBB method. In order to sever my reliance on the pool store, I purchased a Taylor test kit through Watermom's link. I love this kit. While my numbers continue to stay relatively even, the pool store comes up with different numbers each time. It really proves your test results are only as good as the interpreter.

Using the BBB method, I've had stellar results up until last week. We opened around Memorial day to a green hue in the pool, used the BBB method and got it sparkling clear and balanced within a week. Last week we had a heavy rain and the next day awoke to cloudy water and the start of an algae bloom. I had been keeping my FC level in range, according to the best guess chart, and keeping an eye on my pH levels (which were most likely high before the rain).

My numbers before the rain:

FC - 5
CC - 0
TA - 100
CH - 350
CYA - 30 - 35 (I can never figure out when the black dot is considered "gone". At 35, it's only visible if I hold the comparator to my face and squint - it's completely gone at 30)
pH - 7.8+

Before the rain, my pH testing returned a pink-red color. I was working on bringing it back down with some leftover pH Down chemicals I purchased from the pool store last year. After the rain, the FC, CC, TA, CH and CYA hasn't changed much. I'm assuming that my pH was high to start with and the rain kicked the pH too high which, in turn, kicked the algae into overdrive.

After the rain, the pool numbers were:

FC - 3.5
CC - 0
TA - 100
CH - 330
CYA - 30 - 35
pH - 8.0+ (very pinkish red color)

I was able to get my pH into the 7.5 - 7.6 range, and then started the Bleach treatment for the algae. I'm on day 2 of 15ppm chlorine and the pool is improving, but still cloudy with a blue-grey'ish hue. I haven't been able to have confidence in the pH tests since it's likely reading high due to the high chlorine. I'm hoping it's still in the 7.5 - 7.6 range.

So my question: Assuming my pH was too high to start with, will a heavy rain start an algae bloom overnight?

I would like to thank all the contributors and chemical gurus on the site. Without your help over the past 5 years, I would not have had the confidence to switch over to the BBB method. I'm learning more about the pool chemistry, and will have the pool sparkling again in no time.

Thanks in advance!