Have you turned off the aeration and seen the results. It could easily be suspended organic material from the aeration. Could also be plankton bloom. If the jar was left out in the light and it cleared it could be partially suspended clay. It could be dead plankton also.

What is your alkalinity? Take another sample and put a small amount of alum in the jar and note results.

See this

https://srac.tamu.edu/index.cfm/getFactSheet/whichfactsheet/108/

Last edited by ewest; 05/15/14 02:38 PM.