High pH and Low Alkalinity

[dleemtl]

Hello Moderator!
I am in a vicious cycle the local pool store appeared to have lead me into!
1) water green, chlorine good, TA low or almost inexistent, pH good. Advice: add TA (sodium bicarb)
2) TA good, chlorine good, pH too high! Water still green. Advice: chlorine can not be active, therefore add pH - (sodium bisulfate)
3) Go to 1) !!!!

My questions: 1) muriatic acid and sodium bisulfate both reduce pH. Which one does NOT affect alkalinity?
2) How do I get out of this vicious cycle and get clean water??!! This cycle sure is very lucrative for pool distributors! buy TA then buy pH minus, then buy more TA, then more ph - ....

Thank you so much in advance!

[CarlD]

Hi, and welcome!
First off: if your water is green, by definition, your chlorine level CANNOT be good! Your pool store is completely mis-directing you.
Second: Right now, alkalinity is probably totally irrelevant--you have bigger problems.
Third: Alkalinity is relative. When you measure TA, it will rise and fall as pH rises and falls. Both Muriatic Acid and Dry Acid lower TA because of this.
Fourth: Low TA and high pH probably won't be helped by raising TA
Fifth: Your solution is going to be to shock, shock and shock your pool with chlorine, preferably bleach or Liquid Chlorine, until it's clear.

Now, before we can give you reasonable advice on amounts and levels, we'll need the following information which your pool store, with their "advice" probably gave you:
1) FC--Free Chlorine level. The good stuff that kills algae and sanitizes your pool. When you add chlorine, it releases this.
2) CC--Combined Chlorine or Chloramines. Chlorine after it's "used up". Smells like "Chlorine", and the ideal level is 0 (zero).
3) TC-- Total Chlorine = FC + CC. If we have any two of the three, FC, CC and TC, we can find the third. Ideally, TC = FC (because CC should be 0)
4) pH
5) TA
6) CYA--Cyanuric Acid, Isocyanuric Acid, aka "Stabilizer". This is like sunscreen for Chlorine. it's a two-edged sword as is slows the UV breakdown of chlorine BUT inhibits chlorine's sanitizing action. Ideal FC levels are based on the CYA level. Ideal CYA levels depend on your conditions and can range from 30ppm (probably best in Canada), to 80ppm if you live in Louisiana, like our moderator, aylad, does. But we need this.
7) CH--Calcium hardness or hardness. This is important to concrete/tile or other hard-side pools, but for vinyl and fiberglass pools, it's really only relevant if it's too high.
8) Any metal levels they've tested for.

We will also need to know what kind of pool you have: How many gallons/liters, material (vinyl, fiberglass, concrete), indoor/outdoor, brand and size (HP) of your pump, what kind and size filter, and if you have any extras: Heater (gas, electric, solar), water falls or other accessories, erosion systems (Nature2, etc) or inline chlorinator. Also what products do you chlorinate with? Any algaecides you've used? etc.

[dleemtl]

Hi and thanks for the reply. I should have provided more details BEFORE the current situation:

- Inground pool 80,000L, Vinyl, outdoor, 1.5 HP Hayward pump, filter with 4 y.o sand, Hayward heatpump heater, HTC chlorine granules + stabilized pucks, have never had to use algaecide, water has always been clear and clean for as long as the pool existed (7-8 years)

- This year: water was crystal clean after we initially shocked it at the beginning of this season, which here was early April

- All of the sudden, 4 weeks ago, it turned green. Pool store analysed the water, Stab was 50ppm, FC= 3ppm, pH=7.9, TA=10. They concluded that FC, although high, could not operate because of high pH and high stab.

Reasonable enough I thought. So I did what they recommended: Multiple times backwash to reduce Stab, lower pH (sodium bisulf), then SHOCK SHOCK SHOCK as you suggested (I use HTH Ca Hypochlorite 65%), then backwash again. All over a period of 4 days.

- After the 5th day, water still greenish, took sample back to the store: Cya 30 (Perfect they said), FC still over 5 (so unlike you mentioned, FC can be high and water can still be green), CC=0.5, pH 7.2 (perfect), TA=0, CH=250. Their explanation: Because TA inexistent, algae can form easily (really?) so their RX: 1) Add TA+++, 2) Algaecide 60% 1L. Which I did, then water got about 75% better for 2 days and back to the greenish color.

- Another sample to the pool store: FC=still over 5 (off their readings but water still green), CC=0.5, pH=8, TA=60, CYA=30, CH=230, no other metals tested. Their explanation: pH too high so FC becomes inactive. Therefore their Rx: add pH (Na bisulf), then backwash after 3 days..

- Last sample: FC=4, CC=0.5, pH=7.2, TA=10, CYA=30, CH=200, no other metals tested. Their advice: Add TA and algaecide !!! then the vicious and ($$$) cycle!!!

Please forgive me because I want to remind you that
1) I have never had to use algaecide in the past to get my water clear. Ca Hypochlorite has always done the job until they recommended their overpriced 1L for 30$, which I used ONCE under their "advice" and for which the effects (only about 75%, not even 100%) - lasted for 2 days!)
2) The water had always been clean and clear before this last month when this vicious cycle started.

I sure am missing something?

Thank you!