Hi Leila2 and welcome to TFF!
I'm interested to know the extent of your desire to do a "planted tank." Since you went to the trouble to get a special plant substrate and plan two substrate layers and you are aware that CO2 is used in planted tanks, the possibility is raised that really want to launch in to the "Planted Tank" hobby, rather than the "Beginner Tropical Fish" hobby. They have become somewhat separate things and this sub-forum is more about the latter, whereas our planted tank sub-forum is more about the former. Depending on which goal you want most to reach, the startup things you do can make a difference. (more on that later.)
Carbon is one of the 17 or so necessary nutritents for plants but it is a very special one because its involved in the constant production of sugars that transport energy throughout the plant, powering the work done by all the plant cells. Land plants have abundant access to carbon via CO2 in the air. Plants that emerge from the water surface also have this plentiful access. But fully submerged underwater plants have much less CO2 by comparison and, surprisingly, many have never evolved to be as effective at getting their carbon. Helping plants cope with this problem turns out to be a key thing in keeping aquarium plants. In fact, carbon is one of the key skill sets, along with lighting and fertilization and algae.
There are currently three mainstream ways of delivering carbon. One is termed "DIY" and involves do it yourself fermentation bottles to bubble CO2 into the tank. Another is "Liquid Carbon" and involves buying a constant supply of a complex chemical that delivers carbon to the plant in an intermediate organic form it can use. And finally there is the delivery of fine CO2 bubbles to the tank water via a "reactor" or other device powered by the release of pressurized CO2 from big metal cylinders like scuba divers use. Its a no-contest win for "pressurized." This is by far the superior method for carbon delivery, but it has the highest up-front cost and is pretty technical. DIY delivers real CO2 but the process quickly becomes fussy and frustrating. Liquid carbon isn't as effective as CO2 and still costs quite a bit. So all 3 have serious negatives, but the truth is that all fast-growing serious planted tanks are getting carbon delivery to the plants. (There are exceptions, namely NPTs (natural planted tanks, with real dirt) and super-slow-growth tanks, but these exceptions fall somewhat outside what the mainstream calls the planted tank hobby.)
The special substrate you have is a good thing but its better to know now that it will not make up for not dealing with the essentials of carbon, light and fertilization. A good substrate is considered a "backup" addition to a mainstream planted tank, it tides you over if you miss dosing the water with the right fertilizers for a day or if there's a problem with carbon delivery perhaps. Its not a substitute, generally. Its not a main way to accomplish the task of beautiful plants.
OK, so let's get back to why this level of detail matters now, when your still planning and starting. Well, if you were to really decide to make the commitment to attempting a true planted tank, then there is a way to go about it that is a type of "fish-in" cycle, with a lot of plants, and its completely different from what we do over here in "New to the Hobby." If you go over to the planted tank section, the planted guys (Aaron, Dave Spencer, AC and others) can guide you through that process and its a "legit" and really nice way to start a new tank. But it does take some commitment and some expense and time.
If in fact this was *not* what you meant when you said "planted tank" and you were just stringing those two words together and wanted a fairly common tropical fish beginners tank "with live plants in it" then that's a different beast and that's what we do many times a week over here in the beginners section and involves usually a "Fishless Cycle." This too takes patience and time but you've stumbled onto "the real thing" here at TFF, a big collection of lots of serious hobbyists of all types with lots of available information that can save you tons of mistakes.
Anyway, I guess that's enough for tonight and I'm sure the members will pick up on your questions tomorrow.
~~waterdrop~~
ps. Fantastic that you dumped the undergravel filter, they cause no end of headaches for beginners and are even more trouble with plants. Tropical_Fish's advice up there is good, the bottled bacteria products almost never work and are playing on your desire to "get fish quick," which unfortunately is just not the way to go. Understanding the Nitrogen Cycle is a core skill of the overall hobby and in most cases Fishless Cycling is key and a fascinating learning experience.
