Looks like iron deficiency or lockout from here...
IF you poke around the lawn care section of a hardware store, there is a product by Shultz called 'Iron Green' which you can mix up WEAK WEAK WEAK and use as a foliar spray.
But usually your nutrients should have plenty of Fe in them, so I assume that the iron is actually locked out by too much OTHER fertilizer in the soil/nutes or your pH is off.
You can actually run your room warmer than that by the way, up to the low 80s.
So get your pH test kit handy and check the runoff out of the soil. You may also want to flush your plants, and then give them a nice feeding with a complete fertilizer. I'm not familiar with MaxiGrow... what are the numbers on it, and if you read the fine print on the back, does it have a complete set of micros too? (Fe Zn Mg Mn Ca B)