Dave, The land I'm on was an old orange orchard, I wouldn't call it peat because it's dessert, not bog...the only water we get is that which is pumped in from NorCal, or calcified well water (no sulfur). The barley straw is a relatively new addition (since September) and I have this color change every year. I'm not seeing it as being run-off problems, as I said the possible run-off is from a small area that is rock lined and has been well established as a stream year round, and pH is well maintained. It is probably the autumn leaves leaching into the pond, I can't get them all out scooping and picking and it occurs the same time of year, lasts the winter...
I do cut way back on their food but I have always stayed with the Vibrance, I also feed them frozen peas, which they love and I understand that even tho it hasn't much nutrition there are enzymes that help with the slower digestion of the cooler weather; garlic, huh?...My pond never gets below 50*F, we have perfect weather here which is why there are so damned many people!
I know exactly what you are talking about. Same here. I have a very old tree over my pond, I don't think its from the leaves, as I have the leaves falling all year round. But its not like run off (I have had run off and the water was murky from it). We refer to it as 'rain stain'. It also happens in canals and other ponds around here.