Before you add anything take ML up on his offer for Overton to test again. Pull a deep water sample like you sent to me, but also take a "paper towel sample" from the top of your water. In other words take a wet paper towel and drag it across the top off your water (to catch algae). Wrap this paper towel up in newspaper to keep it moist, and send it with your water test (through ML). I suggest this only because of the appearance of your pond on page #6. It appears from the color only that you already have a substantial growth of algae/plankton. Since we really can not judge from the photo alone, Overton should be able to do a microscopic examine of your "paper towel" surface water to see what you have growing. If indeed you already have this growth, and I think you do, then I would say no to the fertilizer. Regardless of the fertilizer issue, in order to get optimum growth you MUST raise your total hardness and alkalinity (refer to ewest's excellent post above). On a pond this small it would not be very expensive to do this. Be it ag lime as others suggest, or the use of calcium and bufferin as I suggest (I am still researching the pros and cons on this one), it is imperative to raise these #'s. Fish do not produce their own calcium. They must absorb it from their water source or food source. With a total Hardness of 17 (or below) your pond currently does not offer much for them. The lower the total alkalinity, the more prone to stress. I use layman terms in the office by explaining it like this:
It is 20 degrees outside, and 90 degrees inside. You stand in the doorway all day long going back and forth between the two temperatures. The stress that this puts on your body and it's immune system is similiar to the stress that the fish go through when total alkalinity in a pond is very low.
Raising the total alkalinity puts a buffer on the water that stops (or limits) the fluctuation of pH and other things. I call it "raising the immune system in the fish." So again, regardless of whether you fertilize or not (depending on what growth you currently have) you do indeed need to raise total hardness and alkalinity in that pond for the good health and growth of the fish.
Where is Cody to explain this better? Again I will state like a broken record that water chemistry is not my "thing". I have a simplistic approach in explaining, but I am still in the learning cycle in understanding.
