Fluctuating numbers

I started battling algae on Saturday as I've previously posted - I uncovered to find algae on parts of the floor and walls but the water was generally clear. During the "battle" process some of my numbers have fluctuated...and not the ones I expected (like Chlorine).

Here's what I've got:

5/26 - water slightly cloudy, but could see the main drain in the 8' end...this is "normal" for my pool as we have sand issues in our neighborhood.

FC 5
CC 0
TC 5
pH 7.2
Alk 90
Cal - didn't test, but it runs right at 50 normally
CYA - didn't test, but had been running right between 50-60
Temp 88

6/4 - uncovered the pool (solar cover) to find algae growing on parts on the walls and floor - water generally clear

FC .5
CC 0
TC .5
pH 7.5
Alk 110
Cal 50
CYA 50
Temp 92
At this point I ran to Wally World and picked up lots of bleach...added amount per BleachCalc to get up to 20. Tested about 2 hours later and got 18 for FC...added a bit more and 2-3 hours later got 20. - Vacuumed & backwashed several times

6/5 A.M.
FC 18 - added bleach per BleachCalc after test
CC 0
TC 18
PH 7.5
Alk 90 ???

6/5 P.M.
FC 15.5 - added bleach per BleachCalc after test
CC 0
TC 15.5
pH 7.5
Temp 92
Vacuumed & backwashed several times again

6/6 A.M. - still some algae growth & water cloudy green
FC 16.5 - added bleach per BleachCalc
CC 0
TC 16.5
pH 7.2~7.5 (color was not either one, but an "inbetween" color)

6/6 P.M. - still some algae growth...after vacuuming water more of a cloudy white
FC 14.5 - added bleach per BleachCalc
CC 0
TC 14.5
pH 7.2
Alk 120 ???
CYA 30~40 ???
Temp 92
Vacuumed & backwashed several times...added DE in skimmer after vacuuming completed until PSI went +1 (started at 14...added until 15 - this took several cups...could be because of the size of my filter???)

6/7 A.M. - water almost completely clear...no algae growth visible - Pump PSI up to over 30! - backwashed & added more DE to raise pressure 1 PSI again.
FC 18
CC 0
TC 18
pH 7.2
Alk 120
Cal 50
CYA 50
Temp 88


The Alk fluctuation numbers are confusing me...until the "outbreak" it had been consistently at 90. My pH has been pretty steady at 7.2-7.5...It's been 7.2 more lately though, so I'm going to add some Borax tonight. The CYA number is bothering me too...Could this small algae outbreak have "eatten" some of it or is it more likely just slight variations in lighting (it's been back and forth from cloudy to bright sun here)?

Hi Sherra;

You should only expect your 'numbers' to be stable, when your pool chemistry is.

When you are in the midst of a major treatment process, for whatever reason, it's normal to see fluctuations.

Being able to independently measure 5 parameters of your pool's chemistry (chlorine, pH, total alkalinity, calcium hardness, and cyanuric acid) tends to create the mental illusion that these are 5 *independent* parameters. But, they are not. What you do to affect one thing, almost always affects another as well. This fact is one reason why I emphasize avoiding unnecessary chemicals: they complicate things beyond comprehension, and make it exceedingly difficult to understand what you need to do to your pool.

In reality, your chemistry readings appear to be quite stable to me. Your calcium is unchanging, as I'd expect unless you did something to either precipitate it (raise the pH a bunch) or add to it (use cal hypo). Your stabilizer can diminish when a biofilm is present, but that doesn't appear to happen. Your one low reading is likely either a simple reading error on a hard to read test, or else a sampling error, such as taking a sample from the zone where you were refilling the pool after backwashing. Alkalinity is HIGHLY affected by small changes in pH . . . and your pH did change some. Plus, it can be affected by large quantities of bleach . . . and it appears that you added large quanties (as you should have done).

But, the reality is that over-testing can provoke over-treatment! I wish I could come up with simple -- but accurate --rules to say just when, and how much to test, but I haven't been able to do so.

What I'd encourage you to do is kill and clean up the algae completely, before worrying too much about the other stuff!

Ben "PoolDoc"

Thank you! I guess a little reassurance that I was doing the right thing is all I really needed. I've not added anything to the pool but bleach and just started adding the DE to the filter last night. I'm hoping to come home to a crystal clear pool tonight. If not, I'll just keep slugging away with the bleach...thank goodness it's only $2.28 for the 6% 1.4 gallon jugs at our local Wally World (I've got 3 in a decent driving distance from me)! I can't even imagine what I'd be paying to keep the pool up if I relied on the pool store. We did that with our AG pool in Kansas several years ago, and we spent several hundred dollars a year in chemicals for a 15' round pool, and the water was never clear. I found this site a couple of months before we moved from there...wish I would have found it MUCH sooner. Knowing how much money we could have saved makes me nauseous. I'm sure we could have easily maintained the pool for about $75 a season.