Now since I got this working, I wanted to do something similar for my 10 gal tank. MagicMagni gets the credit for
this method which I modified a little bit. The
MagicMagni method has three shortcomings in my mind: The contents of the bottles are not mixed, pressure builds up in the bottle because the end of the lines is restricted, and it's difficult to adjust. So here is the product of a few hours toying around with drip irrigation parts:
Bought a 9.99 air pump with two outlets. The air line goes all the way down in the bottle, to get bubbles to mix the solution while it is running. There are four 1/2 gal drippers built into each pressure line, three are reducing the pumps output volume, and one is an open end which also "wastes" some air, and reduces the pressure buildup in the bottles.
Why is pressure in the bottles bad? Because the air volume is compressed much more than the solution, so if the bottles are almost empty, there is a long time of dripping after the pump turned off, until the air is all decompressed. So you end up with a higher dosing volume with an almost empty bottle compared to an almost full bottle. Not good.
Therefore I left the end of the fertilizer line unrestricted, this way once the pump stops the flow stops as well. Inside the bottle there is a check valve which prevents water from siphoning back into the pump. Like with the powerhead method, you just time minutes and mark the bottles to see how much solution is dosed, and adjust if necessary.
Here is the completed setup, ready to be connected to the timer:
I guess similar to switching from DIY to pressurized CO2, going from bi-weekly (me) or daily dosing to this automated solution feels great... (and is much cheaper than the CO2 switch). For those of you who prefer watching their tanks to mixing and squirting fertilizer, consider a similar setup...