Automated Aquarium Fertilizer Doser


If you are using live plants in your aquarium you must remember to fertilize them at regular intervals. Being a bit forgetful, [Deven] automated the process by building this auto-doser.

There are three different chemicals which are dispensed by the system. They are stored in the drink bottles seen above. Each has a plastic tube which runs up to the dosing motors mounted on the black box. [Deven] sourced the motors from eBay. They are designed for this type of application.

Inside the black box is the Arduino that handles timing and switches the motors. The control circuitry is protected using one MOSFET for each. To keep the fish safe the outflow is directed right into the aquarium pump so that the concentrated chemicals are quickly dispersed through the entire tank.

Now that he’s made it this far he might as well add the ability to feed the fish and control the lighting.


14 thoughts on “Automated Aquarium Fertilizer Doser

  1. I thought maintaining plants was a joke till I saw this… verrry interesting! now I’m just wondering how much the fertilizers cost per month and how much a CO2 setup costs to buy and run…

    1. If you go with dry ferts, $25-$30 will buy you a bag of each of the essential nutrients (nitrogen, phosphorus, potassium, and trace mix). My first order of these lasted five years before I ran out of potassium, even after ten years I’m still on my original bag of trace mix. And since they don’t spoil in dry form, the cost over time is negligible. I mix them into liquid solutions, enough for a month or two at a time, at whatever ratios are needed.

      A good pressurized CO2 setup with a decent sized tank will cost around $150-$200 average, I think. I scavenged mine together for less. You can also use “DIY CO2” (yeast fermentation) to produce CO2, which avoids the up front cost. But yeast and sugar cost more than buying an equivalent amount of pressurized CO2 refill, though typically only a buck or two per month on reasonably sized aquariums. And it requires strict periodic maintenance to replace the yeast/sugar mix every week or two when production starts tapering off, because fluctuating CO2 levels tend to stunt plant growth and cause algae. Still, it’s a workable option.

      What I’ve described is a “high tech” setup. Contrast that to “low tech”, which uses nutrient and organic rich substrates (essentially enriched dirt) instead, so no regular fert dosing required. Some CO2 is even produced from anaerobic breakdown of organics. Plant growth is slower, but can still be lush and healthy; the only big downside is that the substrate must be replaced every year or so when it becomes depleted. And there’s many hybrid setups between these two extremes, of course. If you’re truly interested I suggest joining a forum like and read, read, read. ;)

  2. The pumps are made for dosing.
    Using dry ferts and the PPM-Pro method.. $60 in ferst should last me about 2-3 years dosing 8ml/day macros and 8ml/day micros..

    The CO2 has only been setup for about a month now so i’m not 100% sure how long a tank will last yet but my estimate is 6-8 months at about $30 a fill.. so its relatively cheap for a thriving eco-system :)

    The substrate actually has about 1.5″ of organic soil under the eco-complete.. so it started low tech then i decided to learn micro controllers and decided to build this project.

    1. Get a second regulator in there. I had a problem and the regulator failed and I came home to all the fish dead and a CO2 tank that was completely empty. the regulator failed mildly and simply dumped CO2 at a 10X rate into the tank and suffocated all my expensive fish.

      1. Isn’t there enough CO2 in all the air you pump through there? How big do you need your plants anyway? They’re only there to entertain the fish, you’re not growing them as crops, right? Or is underwater horticulture a whole field I’ve never heard of?

        1. It would be enough if it weren’t for the fact that CO2 is 10,000 times harder for plants to absorb underwater (yes, that’s a real figure). So it’s easily a limiting factor, especially if your only source is aeration. A combination of elevated CO2 levels and good water movement helps growth and health immensely. Some particularly beautiful aquatic plants also come from natural environments where the water is CO2-enriched by natural processes, and so are difficult or impossible to keep healthy without providing a similar environment.

          No, the plants aren’t crops, although selling nice trimmings to other hobbyists can make you friends, pay for your hobby, and put at least a little extra change in your pocket. And you don’t have to grow them at outrageous rates all the time. Though there’s a definite initial satisfaction in being able to do so, and it’s useful for initially filling out your tank, keeping up with trimming can eventually become a chore. While limiting growth rate can be accomplished by either limiting light or CO2, doing so by limiting light generally produces the healthiest plants and the least algae. This is a simplified explanation of course, and the whole topic is subject to debate; but should at least give you an idea why adding CO2 is popular.

  3. Might be a bit thick here, but in my setup the fish do all the fertilizing that the plants require. So much so I’ve gotta chop em back to base every two months…..

  4. That looks like a great setup for a barbot, if only the pumps were faster. Do peristaltic pumps come any faster than that? I’ve only ever seen them run about that speed.

  5. barbot – t.. you can get higher flow pumps but they will be less precise… its is trade off.
    for a bar bot i dont think you need to be accurate to the ml so you should be safe with high speed pumps. The rest of the circuit would be identical.

    If you want a nice carpeting plant then CO2 and good lighting will greatly help it along. Plants do tend to grow a little fast and requiring more frequent trimming. IMO a few minuets of work every 2 weeks is worth it for a nice lush piece of living art… and on the flip side i traded some plant trimmings to a local pet store for some shrimp.. if this deal keeps working out it could mean I will never have to pay for aquarium supplies again!! A very nice bi-product if you ask me.

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