We have guppies in our tank and they do the same thing, Occasionally they swim down and flick each other and then return to swimming at the top.

Guppies breed easily and dont need much encouragement (they're as bad as rabbits) they just keep multiplying.

I had guppies that used to stay at the top of the tank all the time as well, i think its just what they do

You might want to keep an eye on the barbs with the guppies though as i believe they can nip fins and that will stress the guppies out!

Any kind of barb isn't really good for a comunity tank. There ok for a while, til they feel safe and then take over. Only you have witnessed that for yourself. Sorry skiped the bit where you said you had barbs. A good fish to get is sail fin mollys, they come in great colours. Keep to live bearers if you want problem free fish. There are others you can add but check it with your fish shop before buying or even ask on here. Sounds like there are alot of people who keep fish.

i keep a tropical tank and find that although my guppies use the whole tank in general,they tend to be more "top dwellers".Some fish(I think Barbs) are known for being"fin nippers"as well,particually if you have fish with big colourful tails(as guppies do)one or two of my siamese over the years have been known to nip and bully at the guppies,whereas my others live with them quite happily.I also keep my tank around 78 temp wise,but again that depends on the fish.Hope you get it sorted out x

I meant to say Last time If youre Pleco's are large you're smaller fish may start to dissappear as mine have, I alway thoght Plec@s were veggies but this is not the case