Need help with grow tent co2 setup!!!

I have been growing for about 5 years on and off indoors mainly and have never run CO2. I currently have a 10x10 Secret Jardin grow Tent iwth Four 1000w HPS under Magnum 8XXL hoods. This tent is where I flower my girls(Black Berry Soda) in Roots 707 mix in 7gallon Geo pots. I use all House And Garden Nutes COCOS A/B etc... I have had good success and harvests not great. I Veg for 3 weeks and FIM top once before flowering. I generally get 1pd per light with 9 plants under each light. The room is exhausted by two 8in can fans and one 8in intake blowing in 60 degree air. I never get the huge nice colas always nice 7-10in long coloas but never more than a couple inches in diameter wet and dried even smaller. Ive tried various strains and never seem to get them to swell up. Everyone is telling me I need to run CO2 so here I am needed help with the setup. Ive had 10 different suggestions on how to do it. I want the easiest low maintenance setup you guys can come up with. Or any other suggestions. Im on day 42 of flower right now Ill put up some pics tonight when the lights go on. Please HELP ME!!

minigen, ppm3. perfect for that size.

What is the SKU number for that? I want exact info on how to set this thing up and how to maintain it.

What controller should I use?

cap ppm3 controller.
they come with instructions, very simple.
it maintains itself, just change the propane tank when needed.