You have two 500ml bottles of yeast solution? If so, that is probably not going to generate enough CO2 to do any good. Generally we use 2000ml bottles, and often more than one of them. Also, you have one too many potential leakage points, by routing the outlet of one bottle into the other bottle. My experience is that the hardest spot to stop all leakage is at the tube to yeast bottle connection. As you have it set up all of the CO2 from one bottle has to make it past two of those connections. And, the check valve you are using does no good. If you remove the second bottle to replenish it, the whole system gets filled with air. Only the one bottle can be removed without dumping the CO2 in the system. https://www.plantedtank.net/forums/sh...503&highlight=
is the system I used, which worked very well for me.