Dave is absolutely right. Be careful about adding too much fresh wood of any kind to your pond in a short time. The tanins (tanic acid) will leach out, and if there's a high enough concentration in your water, it will make it a dead lake - I don't even think frogs will live in it if it's bad enough. I've been told that his test works well, but I just try to limit the amount of fresh wood I put in each year (less than 10 average size Christmas trees per acre) and put in old dry wood and piles of big limestone chunks from the local quarry to supplement that (they have a special pile that they will let me hand load from any time I want totally free).