Why is it difficult? Mine are easy.

Small tanks are much less forgiving. Anything that changes, changes a lot
faster. Evaporation alone can be PITA with a small tank.

Like I said, I've always heard this, but have never found it true in
practice. I maintain my small tanks on the same schedule as my old large
tanks.

But it's a lot of work. You have to choose plants and fish very carefully.
You also need to do so in a large tank.

Not *as* carefully. Many common plants and fish simply won't fit in a tiny
tank. You have a lot more freedom with a larger tank. He wants to keep
angelfish. That is not going to work with a 2.5 gallon tank.

Well sure, and I told him that was a bad idea. But I see just as many
people trying to put an oscar or a goldfish in a 20 gallon too. It's all
the same problem if the the tank is 55 gallons or 5- education.

You have over a watt per gallon. That's plenty for low-light plants,
especially given the short height of a small tank. Where the higher lighting
requirements come in are for high-tech, high-light, Amano-style tanks. Which
is what he seemed to want. (He said he wanted to be able to grow anything he
wanted.)

I've never heard that said before, and I can't even fathom the logic in
that. If I have a 20 gallon tank that has 3 wpg, I should not need more
light in a 5 gallon tank to grow the same plants. especially since it's
likely the tank is deeper in the larger tank. Can you explain this one
more to me?

I have not found that to be the case. I kept a 5 gallon tank for awhile, but
eventually gave it away. It was just too much work.

Just curious, what kind of setup did you have?

I didn't say otherwise. However, it's more difficult to keep the pH stable in
a small tank.

I never had that problem either. Hopefully if your injecting co2 you
know about the KH and ph formula. The same rules apply, and hopefully
you are monitoring and going slow at first. I fiddle with my ph with a
lower KH then most people advise and I don't get fluxes in 24 hours over
..2. Oddly enough, the exact same rate of change I got in my 45 gallon
tank.

You sound as if you're quite experienced with tanks of all sizes. But this
person is a beginner. Remember what it's like to be a beginner? You buy fish
and plants and chemicals you see at the pet store, just because they look cool,
and put them all in your tank. You do water changes religiously for the first
month or two, then might go months without doing one. You buy more fish than
the tank can reasonably support, just because you have to have them. Etc. The
larger a tank is, the more forgiving it is of beginner mistakes, simply because
it's a larger reservoir. Water quality can't change as fast in a large
reservoir as in a small one, and so larger tanks will "absorb" mistakes that
would overwhelm a small tank.

True enough, but he asked if it was possible. He's here asking questions
before he buys, so kudos already. My opinion of what he can do has
increased tenfold then your average newbie. I also don't see a ten
gallon tank absorbing very many beginners mistakes. If he was debating
between a 60 and a 2.5 gallon, I'd understand that.