What are ways to check for headgasket leak

I keep having to add antifreeze to my car. I thought it was the heater core but I changed it and it still goes down. I fill it up and drive about 25 miles round trip and it goes down about a 1.5 inches. It is a smaller than stock aluminum radiator but cools just fine. There is no water in my oil and I have checked my plugs and they all look about the same. I am running cometic gaskets with aluminum heads and studs. Can I just retorque them or do you have to replace them like you would a normal gasket?