DIY CO2
this is just a basic example:
empty clean coke bottle
cut a hole in the lid and push some long tubing through and silcone the edges so theres a secure seal
unscrew the lid and chuck in some yeast and some warm sugar water, screw the cap back on then mix it by swirling/shaking the bottle. place the bottle somewhere and put the end of the tube in the water, wait 10-15m and if you dont see any bubbles then check the bottle for a leak or make sure the bottle is below the tank etc.
i dont know if thats all of it but thats all i can remember