65 liters is about 17 US gallons. Unfortunately, because of your clown loaches, you are already very overstocked. Clown loaches have very special care requirements. This is from a loach specialist website:
"This is a wonderful loach, but too large for most hobbyist aquariums. Allowed a minimum of 75 gallons or more, young Clown Loaches thrive in groups. They require large turnover, efficient filtration systems and current supplied by additional power-heads, frequent water-changes and great attention to cleanliness in the aquarium... Clown Loaches are often sold at the very immature size of 1.5 inches (4cm) or so, but they should not be considered for the smaller (or even medium-sized) aquarium. They will grow quite rapidly from this cute size to around 5 inches (13cm), thereafter the growth slows somewhat, but with good care in a large tank, they can easily reach 8 to 12 inches (20 - 30 cm). They are big, bulky fish at that size...
A potential owner should seriously consider the long-term commitment in purchasing a group of this species, as they will require ever- increasing size of aquaria and may potentially live at least twice as long as some small dogs... Adults will eventually require an aquarium measuring at least 6’ x 2’ x 2’.
Even small specimens of this species must initially be housed in an aquarium that is 4ft long as a minimum. Anything smaller can cause these fast-swimming fish to become stunted and stressed."
http://www.loaches.com/species-index/clown-loach-chromobotia-macracanthus
75 gallons is about 284 liters. And, if you've got common plecos, you're also looking at a fish that will grow well over a foot long. My suggestion is, if you want to add tiger barbs, you should first find the clowns and the plecos a new home. Unless you're planning to upgrade to a very large tank soon, they'll quickly be too big for you to keep alive in the 65 liter tank.
