If the snake does not have any health issues and acts normal, I would not be concerned at this point. Very young greens usually start slow and adjust to new conditions rather slowly also. I would be curious as to it's length for an age reference, but going by the size of the setup you have, I assume that this is a very young snake. A few young greens can be difficult to start, but once they take off, they will rarely miss a meal. We have had captive born neonates go 3 and 4 months before starting to feed and never appeared to have had even the slightest loss in mass. I would only get concerned at this point if it did begin to show a rapid weight loss or started showing a health problem. I don't know if you are offering food at night and leaving it until morning, but anacondas do feed best at night. Don't let the temperature get any higher than 85 if that is for the whole cage. Greens prefer it a little cooler than most boids, low 80's overall with a small high 80's warm area. I personally would not use a pool, but that is your call. If it is spending that amount of time in the water, watch closely for skin blisters as some very young greens are prone to them if they soak extensively. We have had the best luck on chicks, but it sounds like you have tried about everything. If it acts calm like you said, I would refrain from handling it much until it starts feeding, as you are not having to worry about any taming issues. Try offering different food types on a weekly basis and I would expect it to take one within a few more weeks. Good luck.
Kelly