I figured out what was happening with the pictures, but it's too complicated to explain. I need to post detailed 'how-to' post pictures using each of the different services this winter.

Judging from the yellow-green color, it looks like you have fully 'bloomed' mustard algae. Unfortunately mustard algae is notoriously hard to kill.

IF your pool is not leaking, you may want to go the low phosphate route. BUT you have to understand the limitations of this approach:

1. Lowering phosphates *some* is USELESS! It ONLY begins to be useful once your phosphate level is below 0.125 ppm (125 ppb). So . ..

2. You MUST be able to test accurately. For that, you need this: Taylor K1106 Phosphate test @ Amazon

3. Low phosphates do NOT kill algae; it just slows algal growth, making it EASIER to kill or control algae.

4. Many of the phosphate removers sold are over-priced and under-powered. The best is PR-10000, which is hard to find. SeaKlear has a product that appears to be almost as good: SeaKlear Commercial Phosphate Remover For your pool, you'd want to buy 3 quarts, to make SURE you have enough.

5. Using a phosphate remover often clouds the water; you may want to use this clarifier: GLB Clear Blue Clarifier

6. You'll ALSO need to test your fill water. Most tap water has 1 - 4 ppm (1,000 - 4,000 ppb) phosphates added as a corrosion inhibitor. This means you'll need to add small matching doses of phosphate remover EVERY time you add fill water.

7. Removing phosphate is NOT an instant process. The reason seems to be that the lanthanum FIRST combines with carbonates in the water (clouding the water) and THEN the lanthanum carbonate gradually changes to lanthanum phosphate, releasing the carbonates back into the water. This seems to take 3 - 7 days. During this time, if you clean your filter, you tend to lose the lanthanum carbonate on the filter, before it can be converted. So you need to (a) clean the filter, (b) add the PO4 remover, (c) set the pump to run 24/7, (d) wait at least 3 days before cleaning the filter again. THEN, you test the phosphate levels, and repeat if the PO4 level is not below 125 ppb.

8. Total cost on your pool for the kit, PO4 remover and clarifier will be ~$150. Hopefully, you will have some PO4 remover left, possibly a full quart or more.

BUT . . .

9. On the upside, your phosphate levels will remain low until you add fill water OR a phosphate based stain control agent. If you are careful, once the PO4 level in your pool is low, it will only take minimal time and expense to KEEP it low, unless you drain and refill your pool.

10. Once the PO4 is below 0.125 ppm, it will become MUCH easier to kill, and then prevent, algae.