Why switch ferts? Because you want to use a "bloom" fert? The Peter's fert is fine. Check the Tiger Bloom to see if it has magnesium. Looks like either mg deficiency or the plants are just getting close to finishing, or perhaps a pH issue, but most likely it's because you've switched ferts for flowering. I doubt if it helps, and it might be causing this problem. Be aware that plants will yellow as they finish off. I don't know if using dilute nutes is good when the plants are large. You really need a ppm meter and take the Peter's fert to somewhere between 1000 and 1500 as they get bigger. somebody else might have good advice here for you, but looks like bad mg def. I think Peter's has mg in it already. If not you just throw in about a half teaspoon or so of epsom salts per gallon of water, and you can put this directly in the water you feed them; that will work. best of luck. post back what you do so people can see if it works or if I'm full of it.