So I have been cycling my tank and just completed a cycle so went down to my LFS to buy some new fish. I ascked for some assistance and told the shop owner about my tank and he reccomended I get an Siamese shark (After saying I wanted something bigger).He said 4 should do just fine in my 310 Liter tank (Roughly 75 Gallons).So I bought 4 of these Siamese sharks and 2 Seprea Tetra as I already had 4 so they got more friends to Shoal with now. After putting all the fish in my tank I did some research and found that they were actually called iridescent shark and grow massive. Also heard that they will not grow massive in captivity but not to sure if that is true. Anyone know anything about this fish and how big it gets?

310L / 75G
Also have 6 Serprea Tetra now.
They are Grey and have a longish fin under there belly.
Looks like they have 2 tentacles under there mouth kinda like the ones under catfish. They about 5cm now.