First off you have a 'propane cylinder' not a 'tank'.
Tanks are permanent mounted and used in MHs.
The valve you 'really tightened' is the bleed valve. It is a needle valve and you have damaged it by 'really tightening' it.
The leak could be form the bleed valve, could be from the pressure relief valve could be fro any fitting on tank.
You need to use a soapy solution and identify where to leak is coming from.
Then have the problem repaired.....new valves, fittings tightened, fittings removed/cleaned/proper sealant used etc.