Day 6: No significant development.
Whenever the corys move, the serpae tetras go behind them, and then the corys stop moving. Its not like the serpaes are nipping them, they are just following, more interested in the dirt that they disturb in the substrate.
As far as the temperature is concerned, I have been trying and trying to bring it down, but it just won't fall. It's now at 29 degrees celcius. Strange this is, even in the hot days of May and September, the temperature never rose over 31.
So now I have decided to take the following steps:
1) Keep trying to reduce the temperature, slowly, avoiding stress.
2) Remove the serpae tetras for a day or two (in a spare tank) and see if the corys are more comfortable.
3) Put the two albino corys from the smaller tank to the 23gal, (after proper acclimatisation)
I saw the pictures of your corys and they look good and healthy. I think it's just the heat that's got them slowed down. Is this normal weather that will stay for a long time, or just a hot spell? Will it get worse during your summer?
I wouldn't overcrowd your smaller tank with that many corys, but how about moving the 2 corys from there in exchange for the tetras?
Inchworm: Thanks for sticking around and helping me out

I owe you one.
As far as the weather is concerned, it does get warmer in summer, but the tank's temperature doesn't go over 31, only the evaporating increases.
I didn't really understand what you mean by "in exchange for the tetras"...could you elaborte?
PS: I tried to net the serpae tetras out of the tank, but its just impossible. First time I tried to use a net in a planted tank. Looks like I'll have to make a trap.
If I put the 2 corys from the small tank into the large one, then there's no way I will be able to get them out. They're really small, just half an inch

Till then, I'm working on lowering the temperature.