Here is a quick tip for anyone out there.
Install a clay pot in your grow bed right where the water comes into the bed. Why do this? it provides a mixing place for you to add things like calcium carbonate, or iron chelate. The water will mix the additive in the pot and help dissolve it into solution. I find this works well and helps keep additives from clumping up in the grow bed. It also catches snails and unwanted critters and makes them easier to clean away.
There are some who say to bury the inlet pipe under the media so it wont grow algae. This has never worked for me. The pipe constantly gets clogged where the water exits. With the clay pot you get extra oxygen, a place to dissolve additives, and anything that gathers at the water entrance point can easily be removed, even algae.