Most of that guide is really good!
There are a couple of inaccuracies though;
"Well, the answer is that the survival of plants is a must.
Gravel substrate is out of choice for planted aquarium. There are two main options available.
- Inert substrate
- Active substrate"
This isn't true. You can grow easy beginner plants in gravel just as easily as you can in sand. Unless the gravel is really a huge size, more like pebbles than gravel, in which case plants would have a hard time staying rooted. But your normal everyday tank gravel is just as good for growing plants as sand is, both only require the addition of some root tabs now and again for those plants that are heavy root feeders, like Amazon swords and cryptocorynes.
It also says;
"One of the most essential components of a planted aquarium is CO2 supplements. As the plants require CO2 for their growth and survival. In order to provide the necessary amount of CO2 use its supplements."
Also untrue. There's enough CO2 naturally in the tank for most easy, beginner plants. Only some much more difficult, high light/high CO2 needs plants need additional CO2, but I wouldn't recommend messing with that when you're just stepping into having your first plants. It's more advanced planted tank keeping, and mistakes can be deadly to any life in the tank. It truly isn't needed to worry about CO2 levels when you're getting your first, easy to grow basic plants.
I don't use CO2 or liquid CO2 in either of these tanks, never have, and the plants don't mind growing in gravel or sand, and that I rarely remember to add fertilisers!
So don't fret and feel like you need a special plant substrate, a lot of expensive ferts and knowledge, or to start a CO2 system or anything. If you find you love all that stuff and get really into advanced aquascaping later, then great! But for starting out, don't worry about all that! You can have a healthy, well planted, thriving tank without all of that.
Whether to keep your gravel and switch to sand - I'd make that decision before buying plants. They don't love being moved once established, so if you know you'd like sand, then go ahead and make that switch now
You can grow plants just fine in sand.
Also what fish do you have, or plan to have? Because some bottom feeding fish especially, require sand, like corydoras or kuhli loaches, so sand does give you more options for fish. It's also much easier to keep clean than gravel is, trust me! Personal experience with having both
