After about a week of running my DIY CO2 injector on my freshwater tank I've decided I need more plants and more light, I'm really inspired by Takashi Amano's work. The pH has leveled off at about 7.1, nearly where I wanted it. I have a kH test kit on the way to check out my water hardness, it's a good thing to know when messing with CO2. Since my 2 liter CO2 yeast generator is already starting to fizzle out I'll add another bottle in the setup and post some pictures when I finish. Also on the way is a Pollen Glass to diffuse the CO2 into the water a bit better. Currently I have 15W of light from the AllGlass florescent fixture I've had forever, I really want to upgrade this to get around 40W or a bit more. With that amount of light I should be able to grow anything. I only have Anubias Bateri tied to the rocks right now until I get the lighting and CO2 stable. I'll keep you posted.

PID stands for Proportional-Integral-Derivative, it is a closed loop sensor feedback system. It provides smooth and responsive reaction to sensor input changes that allow for robots that can follow, balance, and avoid among other reactions. The process starts with a proportional measurement of error from a set goal. The system attempts to correct for the error by reacting in the opposite direction, proportionally. This alone does not handle changes over time, a change in sensors that changes at a constant rate forces the P section to never reach its set goal. The integral portion of PID Loops allows the system to catch up to the set goal before maintaining a proportional value. The last part of a PID system is the derivative, the rate of change at any point in time. This calculation provides rapid responses to rapid changes. The wikipeida article on this topic is a little heavy but contains images that make understanding PID Loops easier.

I've gotten a lot finished up in the past three days before I head into spring semester tomorrow. I roughly completed a DIY CO2 injection system for my fish tank today. I'm adding plants back into the aquarium and having a little bit of CO2 might help them out. You can learn a lot more about the concept on John LeVasseur's site. Basically I'm using a yeast culture in a 2liter bottle to produce the CO2 and letting it bubble into my aquarium through an air-stone. So far everything seems to be working out, although I'm only about eight hours into the experiment. I started with a rather high pH of 7.6, I'm hoping to lower this to about 7 using CO2. I've noticed a drop to 7.4 since I took the 7.6 measurement yesterday. I'm hoping this huge swing was just due the the vast water replacement two days ago. I'll check the pH in a few hours and see whats going on.