For a low maintenance tank, CO2 (especially DIY CO2) and fertilisation is a definite no no cuz your plants will get all the nutrients from fish food and fish waste and from the substrate when they remineralize, adding CO2 will only disturb this balance in a LOW TECH tank. Plants are supposed to grow slow in a low tech tank. So don't add any fertiliser (make sure you have good kH and GH though) but make sure you've got a base fertiliser though in place from the start (very important). So really the best part about a low tech tank is that you don't even need to bother about CO2 and fertilisation or water change? So let it be and don't worry too much about it and enjoy nature!