Yellow edges

That has helped a lot. I can tell you there is no fan inside apart from carbon filter drawing hot air out, as I found having the fan increased bottom layer temperature, the tent is in a cupboard but can't keep it open for long and having a intake into the cupboard won't be stealth enough, I will try to adjust water pH, I'm on budget. I use liquid based nutes. How can I keep temps low in an environment where it will be hot? Your advice has helped a lot cheers Fire_Farmer

Hello Oftentimes that's a potassium deficiency. But I've also seen it when my ph was out of balance.

Hard to tell from pictures could be any one of many things, it seems to be affecting older growth and not new, there doesnt seem to be rusty spots anywhere, its just the edges that are paling not the whole leaf. If its a deficiency I'd go with potassium but I'd wait for a keener eye to help you on that and I'm more inclined towards it being enviromental. A couple observations to maybe try dial in while you wait for that keen eye to come along..... Day temp - try knock a few degrees off this to be 24-25 celcius Substrate temp - try knock a few degrees off this 5 litre pot could be rootbound, use an enzyme product such as Cellmax Allzymes to help break up dead roots and promote new ones and/or use bigger pots next time. Could be heat stress is contributing to the issue since you mention it's hot near the main cola. No mention of ph, I know a lot of soil growers dont bother and get away with it and I say fair enough if your fully organic it will self buffer but if you are using bottled nutes then to me you should still ph your feeds. Aim for around 6.5 Sorry it's not a definitive answer but usually a dialed in environment helps the plant deal with anything else thrown at it.