I have read on hear temps should be around 20 off and on. My temps are 21 lights on and 15 loghts off. Do i need to put a heater to bring them up a bit. dont really want to but you great people think i shoild then i will. Will it make much difference to yield and quality. Growing 6 grapefrut in all-mix and feeding biobizz organic ferts. the 6 are under 1x 600 hps

Hello mate.

Keep temps at an absolute minimum of 18oC otherwise your start getting nute lock out

yeah id just get one of them little 80watt tube heaters for about 15-20quid to bring it up that extra 5 degrees or so
im pretty sure itd make quite alot of difference aswell mate

optimal temps should be 24-25c lights on. lights off should be as close to day temps as possible, but no higher, and no lower than 18c otherwise nutrient lockout may happen.

a heater isn't absoloutly essential in your case, as it will be warming up soon, but remember the closer you get your environment to optimal, the more your plants will flourish.

Bob

My temps are 17 max and drop to 12 with lights out. I am growing some sk#11 and some other thing and I get no problems at all. in fact all is very well indeed sso I don't have much faith in these temp regulations. My humidity flux's between 50% and 70% . I say if everything looks ok then just leave it be.

cheers peeps, I will stick a tube heater in, money not the problem so i want the best as i can do. will get some pics for you all

Your plants may look healthy, but their potential won't be reached with those temps.