Nutrient Deficiency?

Hey everyone. I have checked out the guides on plant problems, and I would just like to verify what I think is happening.

My leaf edges are brown on the majority of the plant, but not the entire plant. According to the guide, this could be a Potassium deficiency. I'm not sure what course of action to take from here.

I am growing a Cheese variety. Unfortunately I forget the exact strain.

My medium is Roots Organics, I water ever 4 to 5 days, when the medium dries out a bit. I use tap water, and have been using it for two months now without an issue. Every other watering includes nutrients. I am using General Hydroponics three-step nutes. I am growing under a California Lightworks SolarFlare 200, and the light is about 20" away from the top of the plant, 12/12 lighting cycle.

The plant is one month into flowering. Nutes are at full strength according to the directions.

I haven't really had any other issues. I do have gnats, not many, but they are there. I have heard that they don't cause much harm.

Thanks ahead of time for advice.

Pics attached!

Bump. Anyone?

gnats live in your soil before they fly away. It could be damage sure. Over all they look real good. Some flies are attracted to colors try yellow sticky flypaper make sure they are yellow. Hang them up around your plants until harvest time.I think the gnats will go away if you water a little less.

Looks like heat stress. Do you have a good exhaust?

I'd love to see a solid answer with this as well. I've currently got a strain of cheese showing these near identical issues. Also about 1 month into flowering with GH nutrients (though I'm running two-part Lucas formula) under a 600w HPS with good ventilation. I'm stumped. Subscribing for some ideas...

Plants look good basically. You use tap water. You could have a chlorine build up. If using tap water you need to let it sit out for 2-3 day before use. You also might have a micro mute problem. I would flush them with good water. Distilled would be great then feed and add a micro nute product. You can not fix what is done but maybe just stop the progression.

mistake 1.) "I water ever 4 to 5 days, when the medium dries out a bit." let soil dry a lot, not a bit
mistake 2.) "Every other watering includes nutrients" too much; stop feeds. only feed once, maybe twice more, if it NEEDS it.

they don't look terrible. you're half-way to chop.