Hello; This could be. I also am curious about the type of substrate. I do not recall from earlier in the thread. If it is sand then the dreaded anaerobic gas pockets might be the water quality issue.Anyone think a larger pocket of decomposing food and waste was disturbed and released into the column causing a spike since a larger volume of water was removed
To the OP; Is the substrate sand or is it more coarse gravel? Also how deep is the substrate?