I have an older inground pool with vinyl liner. I have growth that starts as a yellow-brown dust and then spread to to have green under the original dusty spots. The growth is only on the horizontal or sloped surfaces of the pool, not on the sides, and it is in shade or sun.

I went to 20 ppm FC (by estimate) with 11 bags of cal hypo shock. The chlorine level was to 3 the next day and zero the day after. I realized that I had no CYA.

I have added 6 pounds of CYA to try to get to 30 or so (yellowish brown on test strip, not quite brown). I brushed the pool. I added shock to get to 12 ppm and it held above 10 on the test strips for three days. Today it is around 5. The pool has stayed green and cloudy since brushing and now I have growth on the pool floor again.

I am unsure what to do because:
Historically, I have used cal hypo tablets and shock. Last summer I used trichlor tabs and apparently got my CYA out of whack.

Last September I had a pipe break and I didn't try to recover the pool for 5-6 weeks. The pool had very bad green algae. I shocked and shocked, maybe 30 pounds. I realized that my CYA was over 100.

I drained the pool partway and added 15 thousand gallons. I have shocked the pool occasionally over the winter, but had no real problems with the lower temperatures I am guessing.

Basically, I THINK that I need to raise the CYA a little more. I am hesitant to add stabilizer, but am planning on adding more slowly. I THINK that I need to add shock to get up to 20 ppm and maintain it for a few days.

If someone could tell me what to do or tell me what other info you need, I would appreciate it.