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post #1 of (permalink) Old 03-26-2007, 05:19 AM Thread Starter
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My Automatic Fert Doser (No 56K)

Ok. I've been asked quite a few times to do this, but never really had the time to write it up. I've been using a dosing system that I set up for about 4 months now. I started using it on my 45G, and then moved it over to the ADA 120P.

The Equipment

It's pretty strightforward. I've got three reservoirs (using two 1000mL separatory funnels, and one 1000mL volumetric flask). I've got a magnetic stirrer to create a "slurry" of Seachem Equilibrium for which the amount I need is not soluble in 1L of water. Three peristaltic pumps deliver the stuff into a "port" on one of the filters' outflow, and into the tank.

So, I'll start with the separatory funnel setup. There are two of them, and this is what they look like:

The funnel is supported on a stand by a ring and a clamp. It's outlet is attached to 3/8" ID Tygon Lab tubing, which is reduced by a series of adapters to 1/8" ID Tygon (same size as standard airline tubing). This connects to the pump.

The setup for the Equilibrium looks like this:

It's a volumetric flask, sitting on a magnetic stirrer. A double bored stopper caps it. Through one of the holes, is 1/8" ID Tygon Lab tubing, the other hole is there to equalize pressure (so the flask does't implode). The tubing connects to a pump.

This is what the whole setup looks like:

It sits in the center of the stand, and the output to each pump connects via 1/4" RO tubing to a check valve which leads (via a series of Y's) into the entry port:

Everything is powered and on an individual X10 timer:

Setting it up to work

Once everything is connected, I need to fill the reservoirs. The micros are pretty simple. The reservoir is basically just filled with a micro solution. I may or may not add iron. To calculate how much KNO3 and KH2PO4 I need (I don't use K2SO4 because I get plenty of K from the Equilibrium), first I need to know how long I want the funnel to last. I'll use 28 days for this example, because I just set it up that way, but once the ADA tank has "stabilized," the macros will be prepared to last 100 days.

Until I can calculate uptake, I'll be dosing EI(ish).


1/2 tsp = 2.8g
2.8g x 3(x/week) x 4(weeks) = 33.6g

So, into a spare 1000mL volumetric flask goes 33.6g KNO3


1/8 tsp = 0.6g
0.6g x 3(x/week) x 4(weeks) = 7.2g

Into the same flask goes 7.2g of KH2PO4

The flask is then filled to the mark (1000mL) with RO/DI water:

And then placed on the magnetic stirrer, and run until dissolved:

Because of solubility issues, Equlibrium is dosed via the flask/stirrer setup, and not more than 30 days worth can be practically prepared at one time. But basically, 45g of Equilibrium is ground in a mortar & pestle and go into the flask, which is then filled with RO/DI water to the mark (1000mL). This goes on the stirrer, which kicks on 2 minutes before the pump begins to draw 30mL of the slurry and feed it into the tank.


Now, when I was using this system on the 45G, the pump outputs were feeding directly into the tank, over the top edge. It was easy to calibrate - I just timed how long each pump took to produce 10mL of product into a graduated cylinder, and used that flow rate to set up the timers.

NOW, the pumps are feeding INLINE, and against the back pressure produced by the filter and the weight of the water in the tank above. I could not calculate flow rates the same way I had previously because the output winds up in the flow of water from the filter. This is what I came up with:

It may be a bit difficult to see it from the picture, but I took a 10mL Class A Mohr Pipette, and attached it to the pumps' input. I was then able to calculate how long it would take for the pumps to PULL 10mL of solution (this 10mL obviously ultimately winds up in the tank).


Now, I've got my solutions in place and my pumps calibrated. Both the micro and macro pump deliver at a rate of almost exactly 2mL/min. Micros are easy, the timer that runs them will turn on for exactly 5 minutes (which doses 10mL) three times per week.

Macros are just a bit trickier. I've got (according to our calculations above) 4 weeks worth of product, to be dosed at 3 x/week. So I've got 12 doses in there.

1000mL / 12 doses = 83.33mL/dose
Pump outputs 2mL/min

Pump needs to run for 41 minutes and 40 seconds, 3 x/week (for this month - like I said earlier, this will change).

Side Notes

I do not have my Auto-Water Changer hooked into this tank yet. The drain line is still plumbed into the filter running my 45G. This filter will actually be moved to the ADA tank to serve as a second filter once all of the fish are moved over. The 45 is being torn down completely. Once this happens, I will not be doing the 50% weekly water changes, but the system will run 10% daily. Dosing will change then as well. Micros and Macros will be dosed daily based on uptake and the water changes.

I am NOT currently dosing Equilibrium on the ADA tank. When I start, I'll be concerned about the fact that the slurry is gritty. If this grit causes the check valve to fail, I will need to think of something else, or the tank will back up into the flask, then onto my floor! This was not something I had to worry about on the 45, because like I said, the pump output just dripped into the tank, it wasn't plumbed inline I'm thinking of putting a second check valve on each input line just for redundancy (will need to re-calibrate the pumps).

If I have any issues with the system, I will report them here!

If anyone has any comments/suggestions/questions, I'd love to hear them!
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