Help! *Very* sudden change in water color!

[UpLate]

This summer (my second as a pool owner) I got lazy on my testing. I use a Taylor test kit. Anyway, the pool was looking great. I had beautiful sparkling water and I took that as a good sign (since last summer my big struggles were with algea), so I neglected testing...much to my current regret.

Then, my liner started wrinkling, and a few days later, my pool surface began pitting. Of course, I was horrified and very concerned! I got out my kit, tested, and discovered that my calcium and pH were far too low. pH was around 6.8 (!) and I couldn't even complete the total alkalinity test because it was way "off" (test turned red before I even added the reagent to make it turn red).

That was Monday. I didn't have any baking soda on hand, but I did have calcium. So I added the calcium. I also turned up the water temperature to 85 degrees for water balancing to hold us over until I could pick up the baking soda.

My wife told me yesterday (Tuesday) that she was inviting a couple folks over, but it turned out it was about ten. They went ahead and went swimming, all of them. Last night I picked up some baking soda and came home and learned about the crowd of folks in the pool. I probably should have shocked the pool then and there, but I was worried about doing anything that might screw with the pH levels that I was about to start adjusting. Pool was still looking good, so I went and just added about 28 pounds of the baking soda.

I woke up this morning to a dull blue pool. I knew right away what had happened. I tested and sure enough, chlorine was 0.0 (both free and combined). My pH was better, but it still was under 7.0, so this is what I did. I checked my automatic chlorinator and saw that indeed, it was out of chlorine. I added tablets, and then I still went ahead and added another 6 pounds of baking soda to further increase pH.

I went inside, and got distracted by other things. Several hours later, I came out. The pool was clear, but blue-green. Crud!

Since I haven't lived in this house but just a couple of years, I am sorry to sound like such a novice. I thought to myself, it is either:
1. Blue-green because of metal corrosion.
But then I thought, why would it suddenly turn this color NOW, when I had begun to get everything back in balance? Perhaps it is a color change related to...
2. Issues from 10 folks swimming in it the day prior.

Hoping it was the latter of the two, because that seemed easier to correct, I shocked it. Then I went in to work (where I am now). It's been a couple of hours, and I just talked to wife on the phone. She said it is worse now...PEA GREEN!

Help! What is my best course of action from here?

[UpLate]

P.S. When I was testing the water, I did something else regretful. I was disposing of tested water in a bucket, but I rinsed the testing tubes with my hose, over by the pool, and I fear sometimes over the pool water. Could this also be the problem?

[chem geek]

The good news is that you don't need to worry about your dumping a small amount of test reagents into your pool water. The bad news is that the fact that your Total Alkalinity (TA) test turned immediately red (after adding indicator dye but before adding titrant drops) means that your pH was at or below 4.5 which is very low and VERY damaging to your liner (low pH is by far the worst thing you can do to a liner). The pH test only goes down to 6.8 so when it shows 6.8 that means it is 6.8 OR LOWER.

In a vinyl liner pool, the calcium level isn't so important. Having 100-150 ppm to prevent foaming is reasonable, but you don't need it high to saturate the water with calcium carbonate (i.e. you don't need to worry so much about the saturation index).

It wasn't baking soda that you should have added, but pH Up, though it was certainly better than nothing at all. You needed to get your pH up in a hurry and pH Up (Arm & Hammer Super Washing Soda; sodium carbonate) is best for that since the TA was also low.

You probably got into this situation because you were using Trichlor pucks/tabs in your automatic chlorinator and these are very acidic so their continued use would lower both the pH and the TA if you didn't add any other balancing chemicals.

Continued use of Trichlor as your only source of chlorine will build up Cyanuric Acid (CYA aka stabilizer or conditioner) in the water and this makes chlorine less effective allowing algae to grow if you don't use a supplemental algicide or phosphate remover (at extra cost). All of this is unnecessary if you use chlorinating liquid or bleach as your primary source of chlorine (with some CYA in the water already). Read the Pool School to learn how to properly maintain your pool.

My guess is that your CYA level is very high. You said you had a Taylor kit, but you should have the Taylor K-2006 you can get at a good online price here or the TF100 from tftestkits.net here with the latter kit having 36% more volume of reagents so is less expensive per test. If the CYA is high, then you will need to dilute your water to lower it anyway so should start doing that even if you add chlorine to try and kill the algae. It will take a lot less chlorine to kill the algae if you lower the CYA level. The shock level is a Free Chlorine (FC) level that is around 40% of the CYA level and you MAINTAIN that level until all the algae is killed and removed. See this post for how a pool full of algae can be cleared with chlorine alone, but only if the CYA level isn't too high.

There are other products you can use to kill algae, but they have side effects. For example, copper-based algicides will kill the algae (though you still need chlorine to oxidize it), but the copper can stain the pool (more of an issue in a plaster or fiberglass pool, but vinyl stains can't be fixed) and turn blond hair green.