If you have a CC of 1, then you are fighting something in the water and need to continue shocking and try and consistently keep your chlorine level at about 15ppm. (How high have you been shocking to?) With a cya of 30, a cl level of 4 isn't gonna kill something growing in the water. I am not familiar with the units you used to measure your hardness level. Another thing I am wondering is whether your pump is too powerful. A 1hp pump is pretty big for a 6200 gallon pool. Too big of a pump on too small of a filter will not filter the water well because the pump forces debris through the filter with too much pressure and your sand can't trap it.