This is nutrient burn.
Baby plants need baby feeding!
There should be enough nutrients in the soil you are using for 4 weeks or so, without the need for any extra feeding.
The fact that only one plant seems burnt is due to genetics, more specifically, that particular plants' genetic need for nitrogen.
Combine this with a too low pH, and you have a recipe for trouble.
6.5 to 6.8 or even 7.0 is more suitable for soil grown plants.
You are also giving them a whole range of different fertilizers, this will not make them grow faster.
Just give them a single grow nutrient and maybe a small dash of a root stimulator, but plants this age and size and growing in Canna soil certainly do not need, B-52, Voodoo Juice, Tarantula and Piranha just yet. Waiting until they are small bushes before they will actually need those types of nutrients would be better.
Hope this helps, Organoman.