noone needs a drop checker. it's just easier. they also don't read changes as fast as they can happen. the smaller the drop checker pretty much the faster the reaction. as in when the co2 goes up sooner after the drop checker will change colors. i know i'm not saying that completely right but i believe the idea is the less liquid and the closer it is to the actual tank water the faster it reads correctly.
you can kill fish with diy co2 in a 20 gallon! i found out the hard way with my very inefficient hagen ladder system with diy co2 mix. that was in a 30 gal.! if i were using a canister to difuse and had no surface agitation i'm pretty sure i would have wiped out my whole tank while i was sleeping.
why do people paint their tanks? i definitely understand the aesthetics of the whole situation. i don't however understand how many people give up on planted tanks and fish in general and have painted a tank they no longer can give away. imo, if you are going to paint it you might as well go all the way and make a background. i used 2.5% limo tint on mine from walmart and you would never know the difference. the best part is for less than $2 i can remove it without harming the glass or rendering the tank useless with harsh chemicals. besides a background looks way more natural, is unique to the tank and can hide a whole lot more depending how it's done. on top of that it can be made in such a way to provide the little niches for individual species without buying, making or scavenging for little odds and ends. i should have done it myself and probably will eventually.
to answer your question... when you have fish you will always need something eventually. it's just part of the hobby.
not necessarily... you have to keep an eye on things until you get it down. you can use the gh, kh, ph table approach, test it with a regent kit or a drop checker. some people go solely by ph and assume a drop of a solid point is perfect. i would not go with that unless you know and understand your water chemistry very well. some people even just keep an eye on their fish and plants but that's the hard way. the drop checker is definitely the easiest.
i would not say diffusing by a canister is bad at all if your canister can handle it which it seems it can. diffusing with a reactor on the output is definitely not bad for a canister imo. i have a few things plumbed into my output as we speak.
i have mentioned this before and will do it again. every tank is different and so is everyones water. when you do co2 start off slow and work your way up to the level you're looking for. if you're going diy (i assume you are) start very low on the yeast. the sugar should be fine with normal recommendations regardless. do not dump in a co2 mixture and go to bed until you know the outcome. also yeast becomes useless slowly over time especially when exposed to air. as you go you will see a need to slowly increase the amount of yeast you will need for your mixture. do not continue with your old mixture once you get a new bag (or whatever) of yeast if you are not using the single serving packets. i forget what size they come in but i think that gets the point across.
Ok, I'll get a indicator off of ebay....I'm still not sure if I should use an elbow, or if I should just stick it into the intake...I guess both would work. Someday, I would like to go preassurized, but for the start off, I'll do DIY and see how my plants do.
As far as the Lbow. You don't have to have it. Its just the thought of a nice clean turn to keep everything tight. As in less hoses tubes etc to hide.
You can just get the end of the hose Under or In the Intake. It doesn't matter how it gets there, as long as the bubbles are going into the intake.
And DO NOT start up the CO2 until you Have Plants In the tank. As in a bunch of plants, as in "planted". Not 2 or 3 little low light plants, that won't use up the normal CO2 thats already in the water.
With that said. Yea, I guess you could kill stuff in a 20g with DIY co2. With no surface aggitation and expecting 1 or 2 plants to use all that co2.
since you are obviously like us normal folk and are on a budget i'd just feed it in the intake for now. as you go most people change things around anyway. you will continue to learn and change things you don't like or seem to get old anyway. even the greats, gurus, and those that make a living at this hobby will all confirm that. if that's what bothers you the most when it's all said and done and you've invested some time and all your patience then you're doing great imo.
try a 30 gallon with around 30 plants overall, no ferts except root tabs, light real low, low kh and an air wall. the ph swing was amazing. 7.6 to as low as unreadable on a wide range ph test kit. it was a long time ago but it was bad! almost forgot... i was using a hob whisper and it was barreling into the water also.