I hate to immediately ask for help, but I couldn't find anyone with a similar problem.

I have a gunite/plaster ~22000 gallon dark bottom pool it has been neglected during winter for a month or two and now we have green algae growth and the water chemistry is all wacky.

Due to a combination of someone adding too much acid and a lot of recent rain the pH is slightly lower than 6.8. I measured the total Alkalinity and it was only at 30ppm. The chlorine was essentially zero.

Mistakenly, I thought that adding Sodium BiCarbonate (Marketed as Alkalinity Increaser) would raise both the Alkalinity and pH. I was wrong, it appears that Sodium Carbonate (Without the Bi) was what I needed. I added the proper amount and raised Alkalinity to 90ppm. I also brushed the pool down and added some 20% algaecide.

Current Condition:

0 chlorine
6.7 pH
90ppm Alkalinity

Questions:

Do I need to fix the pH before I bother doing anything with chlorine?

What can I use to raise pH that won't make the Alkalinity raise as well?

How much chlorine do I add? (I have both pool floater + 3" tabs and liquid chlorine on hand)

When should I be shocking the pool and adding algaecide to deal with the algae?

First welcome to TFP and we don't mind you asking for help. Let us know how you normally chlorinate your pool (tablets, Liquid, etc). Also tell where you're located.

First thing you need to do is read Pool School. You need to get both pH and FC fixed ASAP. You can raise pH without raising TA much by using 20 Mule Team Borax. You'll need about 2-1/2 boxes to bring the pH up to where you need it. Also since you have liquid chlorine and we don't know what your CYA level is I'd shoot for about 7 FC. That'll take about 2 regular bottles or one 182 pz bottle of 6%. If you have stronger than that let us know and we can tell you how much to add until you learn to use the Pool Calculator. You'll need a lot more liquid chlorine than normal because you'll be fighting algae, so stock up.

Once you've gotten things headed in the right direction you need a good test kit so we can help you get your pool chem levels straightened out. I recommend the TF-100 from the link in my sig but the Taylor K-2006 is good too. Be careful if you try to buy it in your local Leslies because they usually only stock the K-2005 and it's not the same.

Once you've gotten a good test kit we'll want you to post a set of numbers and following is waht we'll need.
FC (Free Chlorine)
CC (Chlorimines)
pH (you know this)
TA
CH
CYA

CYA is going to be very important especially if you normally chlorinate with tablets.

We're here to help you so don't be afraid to ask questions.

Thanks for the advice, I've read most of the Pool School, it's really helpful.

I'll try and find a pool store to get some better test numbers. I can't afford an expensive testing kit at the moment. I got the cheap $15 home depot deal.

You still need to know your CYA level. If you can't afford a test kit, you should have a pool store test the water for you and post their full set of results. In the mean time, work on getting the PH up to at least 7.0.

Hi and Welcome -
I'll just add that algaecide is really more of a preventative - and the number one way to kill algae is chlorine and lots of it. When we do recommend algaecide, and that's only a few rare instances - it's Polyquat 60%.

I recommend you don't use the 20% stuff you have at all anymore.

Once you get your PH up... the article How to shock your Pool tells you what you need to do.

Los Angeles is a big place. If you're towards the San Gabriel Valley, I could come by and play with my TF100 kit. PM me if you're interested.

Thanks for the offer Richard, but I found a local pool supply that was able to help me out. I'm in San Fernando Valley so it's a bit too far anyhow.

Went ahead and shocked the pool a few days ago, ran the filter overnight and it's now crystal clear! Levels are still a bit out of whack but tomorrow (with tonight's adjustments) they should be just about right.

Results from the mega-test at the pool supply store:

Free Available Chlorine (FAC) 0.5
pH 7.0
Alkalinity 80ppm
CYA 30ppm
Total Dissolved Solids 1,100
No CH test (they were out of tester fluid )

To help with the FAC, I've added about 3/4 gallon of chlorine
To raise the pH I finally got some Soda Ash and added it, I'll check tomorrow to see how it affected pH and Alkalinity, I also plan on backwashing the DE filter to get all the Algae remnants out.

I think I'm pretty set as far as understanding what to do. My biggest remaining question is regarding how long to run the filter. I've heard "an hour for every 10°F" but it gets expensive to run it so often. Anyone have any recommendations on how often to run filter-pump system, and how the numbers change based on the season?

Anyhow, thanks again guys for the help, this site has been great.

I've never heard of that rule. The general rule of thumb is at least 1 turnover per day, but it's really whatever it takes to keep your water clear and sanitized. I like a bit more than that. Most folks around here "play" with their run times to get the best run time for their situation.

Right now I'm running my pump in two 2 hour segments per day. From 3 to 5 am and again from 3 to 5 pm. During the summer I run it two 4 hour segments per day. 4 to 8 am and again 4 to 8 pm. If we're in the pool during the day I'll manually run it then. You'll have to adjust yours to get the ideal run time per your particular circumstances. A lot of people with peak power rates run it a little during the day and mostly at night when the rates are lower.

I'm not sure you are finished with the shock process. You said the pool was clear and i believe you. But, there could be some more organics hanging around. You FC level of 0.5 tells me something is still consuming the chlorine. Given the time of year, the probable water temp, and your CYA level of 30, I'm not sure the FC decrease ia all due to UV burn off. You didnt post what your shock level was initially, so it kinda hard to tell. At a CYA level of 30 ppm, your target level for FC is 4 ppm and the shock level is 12. If it were me, i would bring the FC back to 12 ppm (use the pool calculator to figure out how much liquid to add) then do an overnight chlorine loss test. I realize you dont have a FAS-DPD kit for measuring FC levels, but if you went out the next morning before the sun hi the pool then took it to the pool store when they opened, you can get a decent idea if you lost much over night. Or, you could use your kit and dilute the pool water with distilled to get an idea what the level is.

There is a good article in Pool School on figuring out how long you need to run your pump.

It was 90F here yesterday, but I'm further inland than he is. Oxnard hit 84F, so he's somewhere in between. When I got home last night about 7:30, my pool water was 64!

This is sunny Southern California, after all!

Wow. Yea, i forget it's summer in some places!

I still think he should try and do an overnight test and get the FC up to around 4 ppm

I agree.