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.
1) Autofeeder
http://www.plantedtank.net/forums/eq...ing-cheap.html
$: 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
http://www.plantedtank.net/forums/di...ro-dosing.html
$: Minimal
+ Very simple setup and reliable dosing.
- Need area of consistent high flow, like inside a filter compartment.
3) Syringe 1
http://www.plantedtank.net/forums/di...icrodoser.html
$: 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
http://www.plantedtank.net/forums/di...fluidoser.html
$: 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
http://www.plantedtank.net/forums/di...uid-doser.html
$: 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.
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Here is a modified version of this!)
6) Airpump 2
http://www.plantedtank.net/forums/di...to-dosing.html
http://www.plantedtank.net/forums/di...-take-iii.html
$: 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.
7) Aqualifter
http://www.plantedtank.net/forums/eq...sing-pump.html
$: About $12 for the pump.
+ Simple and inexpensive setup.
- The Aqualifters output is greatly affected by head pressure.
8) Peristaltic pumps
http://www.plantedtank.net/forums/di...ng-topoff.html
$: About $80 for one pump and an electronic timer
+ Reliable dosing, easy setup.
- Cost!
9) Gravity fed
http://www.plantedtank.net/forums/eq...ty-dosers.html
$: 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
http://www.plantedtank.net/forums/di...g-dummies.html
$: 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.