Common plecy is currently 5 inches. In 18 months he should be 18 inches......see why the other members are kicking up a fuss about suitability? If he isn't at least over 1foot, he will be stunted, meaning that he won't last as long as he should. Common plecos should last at least 30 years, so anything less and you show that you had him in a tank too small for him
The other member was not
change(ing) the subject onto utter bull
as you surgest, they were pointing out a fact that you should have been aware of
Anyhow, back to the matter in hand;
130l, is roughly 26 gallons, so you have 26inches of fish as a stocking maximum for a tank that is less than 6 months old. After that, you can push up numbers to between 39-52inches of adult fish, as a maximum depending on what filtration you have.
Lets break-down the space you have used at the moment, and then look at what issues you may run into, mainly the weakness of the inch per gallon rule when dealing with larger fish;
1 red tail black shark 6inches
1 plec 18inches
1 raphael catfish ?inches, unsure with this fish
3 peppered corys 3X4inches, 12inches
1 silver dollar 8inches
5 tiger barbs 5X4inches, 20 inches
That means that you have 64 inches of adult fish, when all your fish are full grown, not including the raphael catfish. This shows you to be overstocked at present even with fantastic filtration. I would not advise adding more fish to this tank, and would even go as far as surgesting to you that you look for new homes for a few. Depending on the raphael catfish, the tetras may later become a light snack, also, again depending on the size and type of catfish, the tiger barbs may also become a meaty morsle of food
This is all before you realise that the larger fish in there will not obey the inche per gallon rule, requiring more space due to the fact that they are messier than most common community fish.
Please consider reducing the stocking of the tank, rather than increasing it.
All the best
Rabbut