weird leaf burn ?

Hi im 4 weeks into flower and i started to notice a lot of the really old leaves dying off going yellow then falling, but this one had a burn and kind of started from the middle and spread out to one side its done the same on another leaf beside it i was wondering if it was any kind of problem or just the plant using the nutrients up

its in a 5 gallon bucket bottom 1/4 is hydroton as well as the top inch or so (ran out of soil) got holes drilled all around the bottom and lower sides i have it sitting in a saucer which i usually have an airpump constantly aerating the water + a submersible pump directing water from the saucer up to the top refeeding it im using searles flourish as my flower nutrient its a ratio of 16-4-25.7, i tend to keep my ph between 5.5-6.5 when feeding(i use vinegar to lower ph, so tell me if this is bad) but sometimes dont let the water sit overnight ( so maybe chlorine is doing this) i'm just worried its something infectious and if i should remove the 2 leaves most of the older leaves that were going yellow and falling off went yellow entirely then fell/i removed. these two are half green half yellow

taking any suggestions on how i should alter/make my air pump/re-flow type thing better or if i shouldn't be doing it at all and letting it dry out occasionally.

also with the nutrients should i switch to something with less nitrogen? an Australian brand/reference would be nice.
also in the first pic the leaf tips are all spiking up no idea why, its only just started to cool down now in veg it was handling temps between 30-40c and now its steady at 27c so i doubt its that

second/third pic you can see the air pump going down under the bucket with the pump going to top feed.also the other hose at the top is my co2 generator currently haven't refilled that maybe that could be the problem as well.
4th picture is the leaf you can kind of see it in the first picture as well.
second last pic is how i'm keeping her down + stem structure
last pic is just top of a head.
any and all suggestions greatly appreciated, i also have to other baby's i cloned off her in the beginning flowering as well and the ones on the right are later clones i did just before flower.

Looks okay but I would look into different feeding strategies for flowering, you'll want to increase your p levels quite a bit for a feeding or two soon. Your feed levels are probably about right, just need to tweak your NPK ratios.