I have a 1.5 acre pond in PA that was neglected for a while. 3+ feet of muck (mostly leaves, oh and an Atari 2600 joystick about a foot down), lots filamentous algae in the warm months, clarity maybe 6". The previous owner was a sucker for the chemical salesman and it obviously wasn't working out well. I told the salesman to take a hike and last summer I installed an aeration system. 2 diffusers because there is an island in the middle, one on either side. One in about 8' of water, one in 4'. Ran them 12h/day after a gradual introduction. The primary purpose of the pond is asthetic/recreational with some casual fishing.

This summer the water is MUCH clearer. I can just make out the blue bin I put the aerators in on the 4' deep side. Fish are much more active and plentiful. Lots of spawning beds in the spring. Filamentous algae is down by about 65% but I have much more grasses/plants popping up (more than desirable). Probably because they're getting light now.

Now I'm noticing that if I stick an oar 1.5' or so into the muck and give it a twist it releases a lot of gas. Much more than before aeration. From one plunge & twist maybe a pint of gas will pop up. It isn't pleasant smelling but it isn't strong sulfur/rotten eggs either. I haven't tried to see if I can set the gas on fire yet (but give me time).

So the questions are...
Does the gassy muck mean aerobic bacteria is eating it away or no? Since I couldn't see the bottom last year I can't really tell if the muck has reduced. Also, am I likely to have a new problem with grasses/plants? (I'll take that over that nasty filamentous algae that clogs the 1' wide overflow pipe, but I hope they will calm down eventually) Is there anything else I should do to help things along other than give it time?