Help!

[Gvizz]

So I have one leave that has almost dried out and looks like this, the two lower leaves are doing the same, it’s an auto flower plant, any ideas of what I need to do and what the cause is, thanks

 

[Rwise]

Looks like nute burn or PH off, need pics of full plant, watering, feeding, soil etc. etc..

 

[Gvizz]

It could be pH or nutrient burn, this is my first time so it’s all new to me despite doing lots of research!
I water them once every other day, only water one around the top inch is dry, I use water from a water basin which collects from rainwater.
using tomato feed, but admittedly I’m not sure how much to feed them as I’m only feeding 2 plants at the moment.
I have another plant which is only a few days younger which is fine. I can post pictures of the plant later today

 

[Canuck147]

Probably your ph .

 

[Gvizz]

Any tips on how to get the right pH, will a water purifier help?
apparently leaving the water your using outside for 24 hours or so helps?

 

[Canuck147]

I use a pen to test - also have litmus paper.
pH should be 5.5 to 6.5

 

[Gvizz]

I’ve used litmus paper which it seems to look around 6 but obviously it’s not particularly easy to tell whereabouts between 5 and 6 it is, i bought a pH pen but i need all sort of other bits to get a proper reading.