i no longer use a temp gage i have one thats sends temps direct to me in another house but if the plants look good then they will be fine,the reason that i gave up on the ph meter and the temp gage,is we have come a hell of a long way in the indoor growing,from when i first ever did one.
Ditch the temp gage,if the plants have good coulour,i think just go on the plants they will tell you if there is a problem.
Temp gage can cause you to do something,that is un needed same goes for the ph metre un-less you are useing water that is not good for human use.
Same goes for all the co2 tanks and ro water un needed there plants in the end,i think we treat them has though there human on life support nature will allways find a way.i think that you can get a plant to even deal with hot temps the more and more you run it,but the mother room has to be has hot has the flower room,i would only use co2 tanks if i was in a air tight self contained unit.
If you are new to growing then dont get caught up in the latest just get cool hood if you have the money or when you get the money.
i produce oil for medical reasons along with a friend his room runs hot but he still pulls 14 oz min of each plant dry,in a loft space from 4 .in fact he just finished up a grow and got 57 oz dry.every bit went to oil and hash.
something has simple has haveing a 12" oss fan blowing across the tops of the plants can be all that is needed to tek the temps down but the reading would be lower at the plant top then higher in the room.
Try it has long has you have a decent outle/inlet fan then go on the plants,you will get to understand them the more you work with them.
I got caught up in you need this you need that problem after problem all prob caused through me going on what people say the room should be,since i have ditched all the stuff like the two above i hit near a lb per plant dry 99% of the time.
One reading that i do take is the humidity though this is key so you do not get mould,turn the meter on for a hour a week just to take one reading if the weather is pretty much the same where you are at then the reading will most of the time read the same,out door weather plays a key factor in the humidity,
Get the light close has possible during veg and the first weeks of flowering up to around week 4 then higher the light,this will give the plants a wider ark of light.i don't mean feet away at most 1 1/2 ft from the plant tops.higher if you are not useing cool vented lighting.use your hand has the gage to see where the light should be too hot for your hand then its too hot for the plants,
But if you do have abee in ya bonnet about temps
lights on 25/28
lights off 15/18,if the temps are high during lights of the plants will stretch
clones/seedling humidity 60/70 %
vegging plants 55/65 %
flowering 50/55 %