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Auto-dosing Fertilizers – DIY Style

March 24th, 2008

DIY Auto Doser In my last post, I explained how I tested for two weeks to determine the proper amount of fertilizers my 40G tank needed to sustain healthy plant growth, and eliminate algae. With that knowledge in hand, I have now automated my dosing routine on this tank using a few readily available items to build a DIY auto-doser. I cannot take credit for this innovation, as I was following Jeff Ucciardo’s design, who adapted it himself from various designs posted on Aquatic Plant Central.

Building an auto-doser is really quite easy. You only need a container, a powerhead to move the solution from the container to the tank, some airline tubing, a check valve, and a digital timer that is accurate to the minute. You’ll also need some sort of a syringe or pipette to convert the output of the powerhead down to the size of the airline tubing.

For the container, I bought a clear container from the kitchen department of IKEA. A container that is taller will be better than one that is short and fat, as the tall and skinny containers will allow you to more easily differentiate how many days worth of solution it can hold — more on that later.


The powerhead you use has a few basic requirements — it needs to fit in the container, is best to draw water from the bottom so that it will run even partially emerged, and should be strong enough to pump from wherever you plan on storing the unit into the tank. I used the 606 Mini-Jet from Aquarium Systems, and have it set to the lowest setting.

Pipette Sawed Off

To attach the airline tubing to the powerhead, I found that a pipette from Seachem’s fertilizer bottles fits perfectly over the powerhead output if you saw off the large end.

As in any case where you have tubing running into your tank, you definitely want to install a check-valve in the airline tubing to prevent a siphon from forming, and overflowing your aquarium out onto your floor — always a bad thing! I used an inexpensive check-valve from Tetra.

Check Valve

All said and done, I spent $2.99 for the container, $16.99 for the powerhead, $1.99 for the check-valve, and $9.99 for the Intermatic digital timer. I had extra tubing and pipettes on hand, but figure about $35 to build one of these.

Once you have all of your basic components assembled, you need to establish how much solution your powerhead moves every minute, thus figuring out how many total days worth of solution your container will hold. To do this, fill the container with water, and set it exactly where you want it to be next to the tank. This is important because the powerhead will pump different amounts of water depending on the height/distance it is pumping. Now, run the powerhead at 1 minute intervals, using a marker to mark the water level on the container at each interval. Once deplete of water, count the number of marks — that’s how many days you can automate your dosing with a full container. For me, it worked out to exactly 14 days — how convenient!

Now, armed with the previously knowledge of how much I should dose over the same period, I calculated my solution amounts. I put in 100mL of Seachem N and K, and 50mL Seachem Flourish, Iron, and Excel. It’s important not to mix P with Iron in the same container as they interact, so for now, I will have to dose Phosphate separately. Also, for the first time, err on the side of caution, and dose slightly less than what you’d expect. You can always increase it later.

It’s been running for 4 days flawlessly so far, so I’m hoping that this will further help me keep my nutrient levels exactly where they need to be in this tank. I’ll continue to do a few tests to confirm that it’s on target, but I’m looking forward to not having to worry about dosing except for once every two weeks.

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Figuring my Ferts

March 22nd, 2008

Recently, after not quite being able to figure out what was going on with the fertilizers and algae in my 40G, I went on a meticulous 2-week testing schedule, where everyday I tested the levels of the two macro nutrients I suspected were out-of-balance, nitrate and phosphate.

DATE N (ppm) P (ppm) Changes:N P K
Day 1 5 .5 0 (WC) 0 (WC) 0 (WC)
Day 2 7.5 .5 15mL 10mL
Day 3 7.5 .5 10mL 15mL 10mL
Day 4 5 1 25mL 5mL 10mL
Day 5 7.5 1
Day 6 2.5 .25 30mL 20mL 20mL
Day 7 10 1
Day 8 5 .5 10mL 15mL 10mL
Day 9 7.5 .5 10mL 20mL
Day 10 7.5 .25 20mL 10mL
Day 11 7.5 1.0
Day 12 0 .5 30mL 15mL 20mL
Day 13 7.5 1.0
Day 14 2.5 .25 30mL 15mL 20mL
DATE What to add
Day 1 4mL Flourish
20mL Excel
4mL Iron
2.5mL N
2.5mL P
Day 2 10mL Trace
4mL Excel
4mL Iron
Day 3 7mL K
4mL Excel
4mL Iron
Day 4 10mL Trace
4mL Excel
4mL Iron
2.5mL N
2.5mL P
Day 5 7mL K
4mL Excel
4mL Iron
Day 6 3mL Flourish
4mL Excel
4mL Iron
Day 7 Water change

I dose my 40G aquarium using Seachem’s full product line of aquarium fertilizers, minimizing my costs by only buying 2L bottles of fertilizer solution, which usually last me some time. Up to this point, I had been following Seachem’s recommended dosing chart, which for a 40G aquarium calls for the dosing schedule on left.

What I essentially confirmed, when comparing the two charts, is that I was vastly under dosing my aquarium, particularly the macro-nutrients. Over the course of my experiment, as I adjusted my dosing levels according to the test results, hair algae disappeared from the tank. The plants really took off, and were looking much more healthy than before, especially plants such as Blyxa japonica that feed mostly from the water column. Although I didn’t document my trace and iron dosing levels, I found that the uptake of N and P are most definitely limited by the availability of those nutrients, as well as K. This was particularly evident between days 9 and 11, as the nitrate levels stayed roughly the same, even without dosing N. By increasing the dosages of the other nutrients, eventually, nitrate went to 0ppm, and I resumed dosing it.

The knowledge learned in this two week test is going to be invaluable going forward with this tank. More to come on that in my next post…

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