In a heavily planted 125 gallon aquarium with high light and CO2 addition, I add liquid fertilizer almost daily. Problem appears when I go on vacation (or want to sleep a little longer and put some fertilizer in the morning before work ;-) there is no time). The off shelf solutions are pretty expensive so I've decided to give a go peristaltic pump. I made the choice because the peristaltic pump is probably the most accurate method of dosing liquids.
Step 1: parts and tools i bought used peristaltic pump from ebay. Its actually pump itself, gear 1: 150 and electric 12V DC motor. I also bought an electronic timer with a weekly program accurate to 1 minute. Airline enough to reach aquarium and another small piece of pump into the bottle All other bits and pieces that I found work / home: There was a 12V power supply from the dead old Netgear ethernet hub and small pads / skid protectors back from the old hub Small piece of aluminum corner profile Piece of 5 mm plastic ~ 8x13cm Pentium 4 air duct from ATX case ;-) Bottle, the air duct fit in Screws, nuts and washers
Step 2: assembly Basically nothing to say. Assemble everything (as shown in the photos) and keep it as clean as possible, avoiding sharp edges (sand any sharp edges). Counter hide screw heads etc. contributed to make ...
Step 3: adding setup On top of all you need to find out the flow rate. Grab something to watch and measure flow for over a minute. You can syringe measure amount of water, or whatever you know volume or scale (remember, 1g water = 1ml water) My pump has a comfortable flow rate of ~ 5 ml / minute. If you have ready fertilizer (e.g. bought from a shop) and the price did not fit within a minute, recalculate and mix fertilizer with demineralized water.
For example: you have peristaltic pump flow rate 7ml / min want to add 5ml of fertilizer at one time and you have 200ml of the fertilizer, the math is: 7/5 = X / 200ml => X = 7/5 * 200 ml => X = 280 ml, which is the volume of the fertilizer mixture. Now 280-200 = 80 ml you need 80 ml of water with fertilizer to mix the right amount of nutrients in one minute.
If you are making your own fertilizer just recalculate mix and add amounts of powders to water properly. (but if you have enough experience to do your own PMDD I don't need to explain anything) Usefull links: http://www.theplantedtank.Co.UK/PMDD.htm http://www.theplantedtank.Co.UK/Calculator.htm
Now timer, I have about 20 minutes of light on setup, but depends on preferences. You can also find many tutorials on how and when to dose on the Internet. I've sicked the other end of the hose (outlet), the canister filter spout just above the water surface so that water is instantly mixing with the drops of fertilizer. Last step is pipe degassing. Just let the pump run for a while and see if liquid will reach the end of the tube, that's all. Good luck.
Step 4: thoughts The electric motor (or gearbox will need to figure out) is pretty noisy so I need to make a housing for the pump myself. A quick and ugly solution would be a piece of foam. It is advisable to have separate micro and macronutrients (two solutions, two pumps) but in my opinion for my 70L aquarium its complicated. So I keep separate micro and macro and mix on weekly servings. Again, Google is your friend ;-). The price for the whole facility was 1/3 of the brand available in stores so in my opinion worth a try.