Firstly, Welcome to O.S.
I grow SCROG in a 3m x 3m space with 2400 watt HPS
In a 1.5 x 1.5 space I doubt very much that you'll be needing anything like 8weeks veg, in fact I'd be STRONGLY recommending you don't veg for 8weeks.
I say this because when you go from 18/6 to 12/12 there is a massive growth splurt. If you fill your space with veg growth in 18/6 the 12/12 splurt will overtake the space and this is not what you want.
What I do is fill my SCROG net by keeping the growth under the netting and spread her out like a starfish with the plant in the middle, once the plant fills under the netting I then turn 12/12, then allow the growth splurt to grow up through the netting. This gives me straight stems upright for the buds to develop on.
"From some stuff I read it said you want at least 8L per plant in res"
This ain't quite right as there's a few variables that can have an impact here.
Firstly there's your grow medium, some medium holds more water and is slower draining, in which case it can take longer for the fluid to drain. Similarly pot size can play a role here. Adding 8 ltrs in these situations could result in a flood. I have my resi outside of my growspace, so I can check my fluid levels at anytime, but by doing so I have more tubing, so more fluid in those tubes
As the plant grows in 18/6 the water usage is much less than when in 12/12 the water usage becomes much more, but in saying that if your growing one plant, recirc a 40ltr resi should be ample. Well, it is for me So, as you can see the amount of fluid used by the plant can vary
I too run my 'lights on' period at night to try and moderate temps. But something you haven't mentioned is airflow and airflow is VERY important. To grow a plant needs light :tick: , fluid :tick: and CO2.
To get CO2 your plant needs fresh air from outside. Airflow does 3 things, it helps regulate temp, it expels O2 and water vapour waste from the plant/growspace and it replenishes CO2. You want your intake down low, where the air temp is lowest. You want to exhaust vent up high as the hot, used air rises. Preferably you want your intake and exhaust on opposite sides of your growspace so that the air flows through the plant canopy. Now to make sure you don't have pockets of stale, dead air you'll also need an oscillating fan to stir the air within your grow space. Personally I also have an oscillating fan blowing through the canopy. This does 2 things, it moves the air around the plant/buds reducing the likelihood of mould, but it also flexes the stems. Stems are a bit like muscles, the more they flex the stronger they become. You want strong stems to hold up the nice weighty buds that will develop.
Speaking of 'weighty buds', I use 3 layers of netting. My first or lowest net is a steel frame with steel netting, this is to train the growth down and out. Then I have 2 trailer nets above that. The first trailer net is to guide the upward growth, the second is to support the buds to stay upright. Without the netting the buds bend and end up facing the ground rather than facing the light.
Hope it helps
Edited by merl1n, 12 April 2021 - 04:16 PM.