I'm sorry and i know its not what you want to hear but Crossfire is absolutely right, even if we assume the tank is cycled and we assume this chemical product works (which to be honest, i doubt) then this tank stocking is still very inappropriate.
Glowlight tetras - Generally speaking need at least ten gallons
Black widows - Need a larger tank and need to be in a shoal
Guppies - Need a 2:1 male to female ratio
Scissortail - I have these myself and they need to be in a shoal and get way too large, mine must be at least 2 1/2 inches
Penguin fish - Need a shoal and get too big (around 2 1/2 to 3 inches)
This tank is overstocked and the tank can not be 'happily sustaining' the fish as they need to be in properly maintained shoals in a larger tank. I personally would only attempt all these fish in proper shoals in a 100+ litre tank.