alright so i ordered a diy co2 kit (d501) and was wondering a few things.
Lets say i have a 36 gallon tank i want to fill it with plants and also have at least 15 guppys
how much can i crank the co2 before fish start getting affected and what all do i need to keep an eye on
what test kits should i have on hand and how do i set up/buy a solenoid to work with the kit that i purchased
thanks in advance
Where to start
First and foremost, there are great stickies in the Equipment subforum here, and you can read up on a lot of this stuff there.
DIY is not a good choice if you want to "crank the CO2" to the max before suffocating your fish. In a 36 gallon, you'll probably be changing it out weekly, but since you already bought it, you can at least use it to get you a feel for if you want to invest in a pressurized setup.
Rather than targeting the max CO2 your fish can handle, it might be worth considering what your goal is. Are you light limited at all? Are you just looking for maximum growth? Most on here seem to have settled on 30 ppm as a good target for safe but healthy growth. I personally shoot for 15 ppm with DIY CO2 in my 6 and 20 gallon tanks to simply aid growth and color and allowing me to stay light limited.
For test kits, a pH test (do a before and after) will show how much of a drop is due to CO2, or you can use a drop checker with a known dKH. To determine how much of a pH drop you need, you can use the calculator here: http://rotalabutterfly.com/co2-ph-calculator.php
For a solenoid, it's worth investing in the ones designed for our application. The really cheap ones run hot and can get stuck open regularly. To set it up, you'll run tubing from the DIY to the solenoid, then run tubing from that through at least one check valve (I prefer two) to your diffuser.