Want to make a cheap DIY doser for your various aquarium additives? Try using water bottles. That’s right, something as simple as a plastic water bottle can be turned into a great, inexpensive gravity dosing system. All you need to do is drill a small hole into the bottle, insert a piece of vinyl tubing, attach a flow regulating device (tubing pinch or small valve), seal the gaps around the tubing, and add your favorite additive. All of the parts for a setup such as this will run you about $5 at the most, and while it may not be the more reliable dosing system you could add to your system, it will work at least in the short term. When going this route, just be sure to clean the bottle thoroughly before use. Residual liquids like soft drinks can be full of algae fueling substances and can decrease pH to a minor extent.