Increase FC residual to offset poor circulation

I have one or 2 small areas ( about 6-10 sq in) on long side of pool between the pump inlet and the sidewall return about 2.5 ft down that algae begins to show every 10 -15 days. I believe it is a dead spot in the circulation altho I run pump 24/7. Been using BBB for about 1 yr and have been fighting algae on & off. Been using chemgeeks 15% CYA and Ben's shock 30% for control & elimination of algae growth and I have concluded (??) poor circulation may be my problem.
The pool is in-ground 16X32-18,500 gal vinyl lined and my pump inlet (@40 gpm) to pool is 1.5 ft below surface . In addition to the skimmer on the long side opposite inlet, I have a return on the opposite long end of the inlet. The growth appears on the long side 1/2 way between return and inlet. The sand filter nomenclature plate is unreadable however the diameter is about 18" and 24" tall.
Stats today:
CYA=45
pH=7.4
TA=90
FC= 5.5 - 7

My question then is if I were to increase FC residual is it possible to offset the growth due to poor circulation or should I just get in the habit of brushing the area every week? BTW-didn't have this problem before converting last year, however I did spend a lot money on algaecides, shocks etc.

Have you shocked your pool up to and FC of 15ppm and kept it there until the algae is gone, and then for another 24 hours? All you need is bleach or Liquid Chlorine (LC) to do it. 3 gallons of 6% should do it to add roughly 10ppm to your pool.

And what are you testing it with?--the 5.5-7 sounds like a strip.

Carl

Yes. I shocked as you have stated. I use the TF-100 test kit. My nrs were minimum of 5.5 and 7.0 normal. Since the weather has turned cooler my FC loss has been 0.5/day. Overnight loss below .5. I have been adding 20 oz 6% bleach each morning and am maintaining 6.5 FC.

Welcome to the Forum!

While some might find this to be contrary to the usual advice here, I think you are a prime candidate for Polyquat 60!

The bi-weekly dose of poly can, with a weekly brushing, keep the algae from returning.

I'll gladly tell you about how I use poly in the pools I HAVE to maintain at < 4 ppm fc with a cya level > 50. ;)

Please do, I'm quite interested. BTW, I have used Leslie's "Algae Preventer" which is polyquat 60 in the past, but the last few years I seem to have a continuing battle with algae blooms. Perhaps my testing/adjusting needs to be a little better disciplined.
ralph

Hey Ralph!

You're on the right track for keeping algae at bay with frequent testing. I have to test the pools 3X/ day. This allows me to track chlorine loss and combined chlorine rise and dump some liquid chlorine accordingly (when it's below 1 ppm, I add enough to get it to 2+) .

Where the poly comes in is when I find algae spots in one of the pools. I dose with the 2X treatment, after I've shocked and brushed and maintained a fc level of 3 for at least a day - I make sure that there is no visible algae , then add a little less than what they call a 'weekly' dose, every other week. It's worked for me and i hope it will for you.


I'm always willing to talk about pool care with you. :)

Yes, when one has a pool with poor circulation in an area and one doesn't want to have a much higher chlorine level to try and compensate for this, then using Polyquat 60 is an option as is using 50 ppm Borates. These are algae inhibitors with the least amount of side effects.

Okay- getting to specifics do you have any recommendation as to the amount of polyquat 60 vs additional chlorine? It has been an exasperating summer, used many gallons of bleach but perhaps my technique is flawed. Do you have any recommendations for me?
desperate Ralph

Following the dosing recommendations on the bottle of Polyquat usually works well. If you have visible algae growth, start with 16 ounces per 10,000 gallons and then use 3 ounces per 10,000 gallons weekly. Unless your pool is very large or you lose a lot of water from backwashing and splash-out, you may find that using 50 ppm Borates is more economical as it is mostly a one-time cost. For example, for 10,000 gallons, the maintenance dosage of 3 ounces Polyquat costs around $1.80 per week. 50 ppm Borates in 10,000 gallons would need 7-3/4 76-ounce boxes of 20 Mule Team Borax @ $2.50 each plus 282 fluid ounces (2.2 gallons) of full-strength Muriatic Acid (31.45% Hydrochloric Acid) @ $5/gallon so about $30 one-time cost. Or you could get 24 pounds of Boric Acid @ $27.75 per 15 pounds so about $44. Again, this assumes 10,000 gallons so scale up or down accordingly.

I just add the start up dose and then supplement with the weekly dose.

With the pools I care for, I have to check combined chlorine every day - if I see it start to rise, I add a gallon of 12.5% and then add the suggested bi-weekly dose of poly a few hours later (having brushed the low circulation areas).

The other solution I had, before using the poly was to brush the low circ areas daily, while maintaining < 4 ppm fc limit max that law requires for commercial pools.