I have a 55 gallon tank with two aqua tech 30/60 hob filters. It's mediumly planted with some rocks, goldfish and ghost shrimp. Its been up and running almost 4 months. I just got some test kits, my pH is 7.5 and my kH is 4 so that means my Co2 is about 4.7ppm, right? Should I add Co2?
You could be close as the co2 concentration of a non supplemented tank can only match the atmospheric concentration, which is roughly 3ppm. However, the optimum levels are 25-30ppm. Tanks could ALWAYS use co2 supplementation. I second the notion that those charts can easily give false results.
Also, how are you keeping shrimp and goldfish together? Shrimp are tropical and goldfish are cooler temp fish.
I just got the goldies to build up the bacteria and make sure my young kids didn't fill the tank with cookies and kill everything. I'd rather lose a few goldfish to cookiecide than some more expensive stuff. They're amazingly well behaved, they haven't touched the plants nor the shrimp and the shrimp are doing amazing. I plan on swapping the goldies out for some nicer fish in a few weeks, the man that runs the local fish store said he'll find them a nice tank at his shop when the time comes. I have some pictures in my profile.
If it is working, it works. I tend to try things that many tell me won't work. Whether to add CO2 will depend on what you want from the tank. If you like simple and it is running okay, why bother? If you want more/better plants or growth, more CO2 is likely to be good.
A balance of things is needed. More light may require more CO2 requiring more ferts. At what level to stop? Personal decision.