Whereas the normal shock level of an FC that is around 40% of the CYA level works well for normal green algae, it takes an FC of around 60% of the CYA level to more quickly kill (for shocking) yellow/mustard algae. So for your 30 ppm CYA, that's an FC of around 18 ppm, so not far from what Al suggested.

You need to keep that level up for an extended time such as the week Al suggested and you need to put in any poles or other equipment, floats, etc. you sometimes put into the pool. You may also need to check behind light niches and remove handrails (if removable) or any other areas where there may be water that doesn't circulate well.

This all assumes you actually have yellow/mustard algae and not just dirt or pollen. If it tends to grow on the shady side of the pool, it is more likely to be yellow/mustard algae. Dirt feels gritty, pollen feels mushy, and algae usually feels slimy.

As for a chlorine test, you can use the dilution method Al suggested, but for even more accuracy you can use a FAS-DPD chlorine test. You can get such a test here (the full TF100 kit is somewhat similar to Ben's kit and also related to the Taylor K-2006 and uses Taylor reagents).

Richard