How close are the lights? If you can get a clearer pic i would be able to see discoloration in leaves. Maybe you should replace your hydro system with clean water, flush it out a little. It looks like if theres only 1 spot this can be harmless
yea looks like overfertilizing but plants have so many problems back to back iif you forget to do things the plants may suffer but you can easily correct it if you catch it in time plants still looks fine to me if you ever get scared think your plants dyin one drop of superthive tp be safe or 2 drops every 3 gallon of 1 drop per gallon grow so many roots than your plants are takin in the nutes again and water the while the old roots recover
i would trim it to snip of the tip or leave it your choice yea butt like jess said flush it next time you give it nuted give it less than yu did last time
looks to me like a litttle heat stress happens when your lighst to close they bleach yu plants and turn them yellow and they could kill ur plants if you have algea also superthive should take care of that alow it to grow new leaves