Over the past years, several people have introduced autodosing methods and more or less successfully used them. For future reference, here is an overview of these solutions, along with some personal opinions with regards to cost and advantages/disadvantages of each method. I will update this post as new ways are discovered, or edits become necessary (let me know if there are any errors or omissions). If you have questions about specific methods, please post them in the threads for that particular doser.
Autodosing on the cheap
$: About $40 for the Pentair Aquatics Lifeguard feeder
+ Simple setup. Dry mix keeps nutrients from degrading.
- Integration into hood (sump would be advantageous). Moist air will clump fertilizer, might not work reliably. Fertilizer powder getting into the feeder will destroy the mechanics over time.
2) Test tube
Easier macro dosing
+ Extremely cheap. Very simple setup and fairly reliable dosing.
- Needs area of consistent high flow, like inside a filter compartment. Over time, biofilm can grow, or detritus can fall into the tube, reducing the amount of dosed fertilizer.
3) Syringe 1
$: About $5 for mechanical timer, oral syringe and some small parts.
+ Good for very small doses
- Somewhat complex to build. Plastic syringes don’t last long. Dosing adjustment not very flexible. Needs strong timer motor.
4) Syringe 2
$: About $10 for mechanical timer, syringe, checkvalves and some small parts
+ Easy to adjust in a small range. Minimal maintenance once it is working.
- Plastic syringes have limited lifespan. Depending on checkvalves, there could be some back-syphoning if the bottle is underneath the tank. Somewhat complex to build.
5) Airpump 1
Cheap DIY liquid doser
$: About $20 for an airpump, some tubing, and an electronic timer, $2 more if using checkvalves.
+ Very simple setup. Minimal maintenance once it is working. Very easy to adjust dosing over a fairly wide range.
- Difficult to get the needle holes to be the right size. Liquid (bubbles) remaining in the tubing might prevent refilling of the coil. Small changes in dosing depending on fillstand of solution.
(Here is a modified version of this!
6) Airpump 2
$: About $22 for airpump, some tubing, checkvalves and an electronic timer.
+ Reliable dosing once the rate is adjusted.
- Mixed solutions might degrade over time. Changes in dosed volume depending on fill volume of bottles.
Cheap dosing pump!!
$: About $12 for the pump.
+ Simple and inexpensive setup.
- The Aqualifters output is greatly affected by head pressure.
8) Peristaltic pumps
DIY Automated dosing/topoff
$: About $80 for one pump and an electronic timer
+ Reliable dosing, easy setup.
is a link to an excellent DIY peristaltic pump!
9) Gravity fed
$: About $25 for the Kent unit and some tubing, ?? for an IV bag from your hospital.
+ Simple setup
- Difficult to place, unless a sump is used. Settling and degradation of solutions might occur.
10) Water Pump
Autodosing for Dummies
$: About $22 for a water pump, an electronic timer and some tubing.
+ Simple setup. Very reliable dosing. Minimal maintenance. Good adjustability.
- Solutions might degrade over time.