Question about planted aquarium and fishless cycling

Algae is a little more under control since a good cleaning and 40% water exchange. After reading the articl on how to get rid of algae and talking to a kid at the pet store about CO2 systems, I decided to go ahead and add more plants. I should have checked my KH first. It's 8 and with my pH of 8.2 I am guessing I am killing my plants. My other water peramitors even before a water exchange when I had missed a week of doing an exchange have been perfect. I guess I am a bit afraid of setting up a CO2 system and starting it. What system do you recommend for my 46gal tank. I have read reviews both good and bad on the systems I could find on Amozon. My local pet store doesn't even carry them. I have a family of 6 with 4 kids always on he go with sports almost every night of the week and weekends away with traveling baseball. I would like a reliable system.  I am thinking of a DIY system, found supplies for one that has instructions on Amoxon for $12.70.  
I am really excited about how well my fish are doing. It's a busy little aquarium now. Finally got some more guppies to keep my 2 that were born in my tank company. They are swimming all over the tank again. I do have one Molly that spends a lot of time in the evenings just sitting in one place. It started out on the bottom of the tank behind stuff but now she sits mid tank level. Every now and then another Molly will come by and nudge her and she will swim a bit then go back to that same spot and sit. She is still eating.