Help! How do I clean these stains? Can't hold chlorine.

[orzsol]

I think these are from caterpillar poop?? Gunite pool, keep shocking but chlorine is down to 0 again. pH 7.5.

 

[Texas Splash]

To help clarify your thread, I'm going to modify your title but cut & paste some of your description into the first post. It's odd that you said you have shocked but have a chlorine level of zero? We can guide you through some options for detecting the type of staining, but we first need to know how you are testing the water. Which test kit specifically? And can you provide a full set of test results please?