First off, welcome to AQ! and from the looks of your post, planted tanks! I can't really answer any of your questions though you've got a HUGE tank compared to the rest of usOriginally Posted by otakbun
Anyway, it'll help us help you if you told us what exactly you're trying to keep.
1) Do you have any specific plants in mind? or are they just for your fish? And you aren't putting liquid CO2 into your tank. That's physically impossible. And would also freeze the water. "Liquid CO2" is found in the CO2 tank as it's under high pressure. It then goes into the regulator where it is brought to normal pressure and becomes CO2 gas. Then it's pumped into the tank where is dissolves into the water to be absorbed by the plants.
2) Enough light is the bare minimum. 2 watts of lighting per US galon of water is enough for most tanks.
3) How big are these pebbles? and how deep is it? pictures would really help. But for now, i think you'll need to buy substrate. A cheap one would be "lapis sand" most shops should carry it. Try to get grains between 2 and 5mm Usually anything bigger than 5mm will have gaps between them too big for the plants to root. Anything smaller will compact and crush the roots of the plant.
After you but it, wash and then fill your tank to about 3 - 10cm deep and start planting. There are more things you can do like base fertiliser and things like that but.. that's really quite optional.
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