I did a water test of my pond's chemistry this morning.
From left to right PH=8.0, Ammonia=0, Nitrite=0, Nitrate=0, Phosphate=5
pond has been established for about 7 years and is pretty much care
It always surprises me is now low my Nitrate levels are.
It's a 1300 gallon pond containing about 70 pounds of fish
which I feed 20 oz of food to every day. The Nitrates are being consumed by about a dozed 1 gallon plants in a stream (NFT - Nutrient Film Technique).
It might be because this pond has been established for so long, but it never needs any adjustments. I let the PH ride on the high side because it's more about being a Koi Pond, and the garden is just a benefit rather than a product.
My Other systems are relatively new, and I'm attempting to find a balance between fish and plants. The PH buffering has been a difficult obstacle, and I may reduce the amount of rock in these systems to see if it becomes less of an influence.
My newest system is a combination of gravel bed and raft. I'm beginning to prefer raft systems over gravel, but I like the idea of keeping a little rock in the bottom of the raft tanks. If buffering continues to present a problem I will convert the gravel bed to a raft tank.
I plan to purchase a test kit for water hardness in order to make a better assessment of the buffering. Ideally I would like to keep my PH at about 6.8 in order to promote iron uptake by the vegetation.
Kobus Jooste wrote a very good article about water chemistry last year.
Here are some more links: