Blazinkill504: From the questions you're asking I assume that you're new to growing with an Aerogarden. I would suggest you read everything you can get your hands on at Aerogarden's web site and the manuals that should have come with your unit. If not, they're available on line at their web site for free. Get to know the folks at their 800 customer service number, just don't tell them what you're growing. If it's the seven hold model with the tall, (24"), arm/light stand and a hood with three flat high intensity CFL's you should be good to go. Just don't try to grow more than two plants in it or it'll be more work than it's worth.
And yes, you'll have to check and adjust pH everyday. You reservoir only holds 112 ounces and once you plants start gobbling up your nutes the pH will change radically. All the more reason to have a good relationship with a local hydro store.
Figure on changing your nutes weekly and giving the reservoir a good scrubbing. Close off the unused holes to keep the light out and that will prevent algae from forming. Put in an air stone fed by an aquarium air pump with a one way check valve to protect the pump in case of electrical failure.
CO2 tablets? I haven't heard of that but you do need to feed the air somehow into the reservoir.
Since you asked about nutes, please let me put in a plug for Technaflora's, "Recipe for Success." Discount Hydroponics at Riverside, California turned me on to it about three years ago and I haven't looked back since. If you have a set of measuring spoons and some type of a pH tester you'll find they're complete and very user friendly. They have a sample test kit for about $30 that will last you a long time in an Aerogarden.
That was the good news, here comes the bad. Everything with Aerogarden is proprietary, meaning it is a patented, self contained growing system and almost impossible to get parts and services from anyone else, but I still love all three of mine. Your supplies are available at Aerogarden on line and at their 800 number. I suggest you buy them in bulk once or twice a year to save on shipping. Their shipping is generally slow so don't wait until the last minute, especially at this time of year with the upcoming holidays.
You can get a Master Gardener's kit that has enough cages, grow plugs/pods, (Growing medium), labels and humidity domes for a couple of crops for the seven holes unit. After a trip through the dishwasher you can reuse the planting cages but you'll need new grow plugs, labels and probably humidity domes. You can buy them in bulk a lot cheaper. I recommend you don't try improvising because I've had mine for over five years and nothing I, or other Aerogardeners have encouraged me to try worked as well as what A/G produces and sells. Also, what's your time worth?
A few words to the wise: don't try to grow more than two plants in your A/G and always have a spare pump and filters and lamps handy.
That sponge filter won't keep much out of the pump except maybe boulders. Wrap your pump and tower in a pump sock from a hydro store, ($10 to $15) or carefully stretch a short nylon sock that women wear with flat shoes over you pump and tower. Those socks are $2 a pair at Walmart. Otherwise you'll likely have roots entanglements that will kill your pump in the middle of a grow.
You want to use good water, not necessarily distilled, but nothing that will react unfavorably with your nutes. Most tap water sucks. R/O'd water is always best
Last but not least, keep it clean. You can remove the spars from the reservoir, they were only there to keep its shape during the manufacturing process and shipping. Once they're gone it'll be much easier to disassemble for cleaning because the roots won't have anything to get tied up to. I hope this helps. HSA
