This nute burn or something else?

These 2 plants, different strains being grown under the same conditions have these burnt spots on the leafs. To me it appears to be nute burn but i just wanted others input on it. Also i have been feeding pretty light this go around and using veg and bloom nutes to not N starve the plants in flower. Base water is ro mix with some tap to a ppm of 150-200ppm then after 3ml of grow nutes and 5ml bloom i get about 300-400ppm depending on what my base water startes at. Ph of water and nute solution is 6.0. Temps are in the upper 70s°f to low 80s°f. Medium is roots organic soil in 5g cloth pots.

Pics?

Sorry high and spaced them. Edited.

it looks like fertilizer has been dripped on the leaves. if this hasn't happened, the either it's genetic flaw or physical damage like rubbing the leaves, or it's bugs.

Looks like light burn in some spots

I water feed at the base of the plants and the dry brown areas are at the tops of the plants and these are 2 different genetics. They are bag seed though so unknown genetics. I have seen no pests at all, this is a new setup done clean. I doubt it is light burn since i was running t5 ho lighting and unless the plants touch the bulbs its almost impossible to burn them. I noticed this when i pulled out all my plants to put in my new 600w hps light.

What is your soil ph like? I know you recently started using RO and tap mixed for 150-200ppm. I forget if you stopped ph'ing your nutrients too? If so, maybe that's not working out as expected.

It kind of looks like pictures I've seen of root rot. But, you don't seem like an overwaterer. Have you noticed gnats?

No pests at all that i have seen. I have have just abiut every pest you can get in the past. This was a new clean setup from seed. I do still ph the water to 6.0, my tap water ph is pretty high after mixing ro tap and nutes ph is 7.0. Last time i checked run off ph it was about 5.8-5.5. There has been no new issues or further dead dry spots. It is only on the tops of 2 plants and they are the tallest. I did have them 2-4 inches from the t5 bulbs which were hot to the touch and have burned tops in the past. Also have some curled leafs to the top near the leafs with the dead spots. Oh yeah also i dont over water for sure in fact i am guilt of u der watering a few ti es this go around, these are some thirsty ladies. I have always cautch it in time when they are droppy and within 20-30 minutes of water they have always perked right back up. I gues it is possible i did a little root damage though if they got too dry....

Humm I think Imay have N toxicity. I have been using grow along with bloom this time and im mid week 3 of flower. All my other leafs are a dark green some even have a shine to them so i already new i was pusging the N a little too much. My last 2 watering have just been phd water to flush out the soil and let the plants use up the N. No more N i think from now til harvest. It does look a lot like root rot but t here is just no way.

Well i hope i have the N issue under control. I water with just phd 150ish ppm water for 3 waterings and today i water with 1.5 ml flower and 1 ml liquid kool bloom. Lost some older lower leafs, they were not getting much light anyways. We will see what happens.