Gotta leave in few minutes, so let me give you some stuff to get you started.

1. Blue-green colors in pools are almost always from copper. Mostly likely your low pH has dissolved some of your copper.

2. When you have high copper, high pH OR high chlorine can cause the copper to stain your pool.

3. The 'alkalinity powder' probably caused some of the copper to come out.

Do ALL these things:

1. Adjust your pH to 7.0 - 7.2. If you need to raise your pH, use borax and NOT any other chemical!
2. Keep your chlorine fairly low, and do NOT add a large dose all at once.
3. Run your filter 24/7.
4. Buy some HEDP (to keep the copper dissolved) and some polyquat (to keep algae out while the chlorine is low).
5. Get a good testkit ASAP.
6. Complete the Pool Chart
Pool Chart Entry Form
Info for the other steps, below.

Ben

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+ Get a cheap OTO (yellow drops) / phenol test kit, or if available at YOUR Walmart (check availability), get the HTH 6-way DROPS test kit, which is compatible with the Taylor K2006. Test the pool as soon and you can, and post the results. If you get the 6-way kit, ALSO test the water you FILL the pool with, especially if it's a well, and post THOSE results as well. (The HTH is the best available kit you're likely to find locally, but it's not the K-2006. It can only provide rough measurements chlorine levels above 5 ppm, and it measures "TOTAL" hardness, rather than "CALCIUM" hardness, which is not ideal.)

+ Having a good test kit makes pool care easier for EVERYONE, but is an ESSENTIAL tool for pools with problems. A good test kit means a kit that can test chlorine from 0 - 25 ppm, pH, alkalinity, calcium hardness, and stabilizer with reasonable accuracy. Test strips (AKA 'guess-strips' ) do NOT meet this standard. Some pool store testing is accurate; most is not. The ONLY way you'll know whether your pool store is accurate or bogus, is by testing accurately your own self. On the other hand, pool store 'computer' dosing recommendations are NEVER trustworthy -- ignore them. They are designed to sell more chemicals than you need, and WILL cause many pool problems.

+ We recommend the Taylor K-2006 test kit, which meets the requirements above, for many reasons. The HTH 6-way drops kit is a great starter kit, and is compatible with the K2006 (it's made by Taylor). There are a few alternatives; for example Lamotte makes an FAS-DPD kit that's OK -- but it costs 3x as much. But, we're not aware of any test that is better, and since we are all familiar with the K-2006 (and can help you with it) we recommend it exclusively ( Test kit info page )

One caution for the 2012 season: Amazon does not stock the kits directly. So when buying at Amazon, Amato is our current preferred seller. However, they often don't list enough stock to last the whole day, so try order mid-morning. You should expect a delivered cost under $60 for the K2006A and under $95 for the K2006C. If you can't find that, wait a day.

+ Here are links to the kits we recommend (you can check local availability on the HTH kit, using the Walmart link):
HTH 6-Way Test Kit @ Walmart
Taylor K2006A (3/4 oz bottles) @ Amazon
Taylor K2006C (2 oz bottles) @ Amazon
+ Borax => 20 Mule Team Borax from Walmart or elsewhere

+ Chlorine is the strongest algaecide you can buy . . . but occasionally, you may need a different one. Almost the only alternative algaecide we recommend is polyquat -- poly [oxyethylene (dimethyliminio) ethylene (dimethyliminio) ethylene dichloride] . This product is a GOOD clarifier and a moderately good algaecide, with almost no bad side effects. We often recommend it for use when you are going on vacation, or when you need to lower your chlorine, to prevent remove stains. It has become quite difficult to purchase locally at the normal full strength 60% concentration. If you find it locally, at a 60% concentration, that's fine. But be SURE to check the chemical name. If you need to buy it online, here's an Amazon link:
Kem-Tek 311-6 Pool and Spa 60-Percent Concentrated Algaecide, 1 Quart
+ HEDP =>
Jack's Magic Blue Stuff (20% solution)
Jack's Magic Purple Stuff (20% solution)
Jack's Magic Pink Stuff (60% solution)
ProTeam Metal Magic (30% solution)
RamChem Ram Metal Hold ((60% solution? )
Kem-Tek 338-6 Metal & Calcium Eliminator (20% solution)
Haviland Stain & Scale Magic (30% solution? )
Jacks Magic The Pink Stuff 1qt (60% HEDP) @ Amazon
20% KemTek HEDP @ Amazon