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AquaPonics, Plants, Hardwater, Amonia, Nitrates, and cycling

13 years ago

Its been along time since I've had an aquarium. It seemed like every time I tried having one, my fish always ended up dying on me. I attribute that to my ignorance on proper maintenance.

Recently I learned about aquaponics (a form of hydroponics) and how tank water can be used as a nutrient source to grow plants. I read that when an aquarium is used to grow plants the fish tend to be healthier.

I will be keeping a grow tray above the thank and water will be constantly pumped through the tray and fed back into the aquarium. Since gardening is a love of mine I figure I would give having an aquarium another run. I don't know how many people here would have the experience to answer these questions, but its worth a shot!

Hard water - I live in a hard water area. How bad is hard water to fish? As plants take in the nutrients, will they absorb the minerals in the water and soften it? It seems like it should since plants use minerals, but I'm not sure if the minerals in hard water are in a form plants can absorb. If the minerals in hard water are not usable to my plants, what can I use that is non toxic to humans to soften the water? I read baking soda is a good alternative? How can I use baking soda in a 20 gallon tank?

Ammonia and Nitrates - These are nutrients plants use for green growth. I'm starting with green leafy vegetables like lettuce (light feeder) and spinach (a heavy feeder). Lettuce likes its liquid nutrient source to be around 560-840 ppm and spinach likes 1260-1610ppm. With that said, and providing there is enough plants in the tray, I shouldn't have to worry about ammonia and nitrate levels right?

Cycling - With the plants there to absorb nitrates and possibly ammonia, do I still need to worry about cycling the tank, or is cycling still necessary, but speeds up the process?

Partial water changes and gravel siphoning - Will I still need to do weekly partial water changes? Will a monthly siphoning of the gravel still be a necessary chore, or does that depend on filtration and how clean the fish like its water to be?

Comments (7)

  • greystoke
    13 years ago

    Hi greenthumbdewd,

    Those are a lot of questions, but IÂll try to answer them as best I can.
    Besides that . . . I think I know why your fish died. They died of poisoning. You need to urgently educate yourself on water chemistry.

    1. Water hardness is caused by calcium and magnesium salts in the water. Usually in the form of bicarbonates and sulfates. Plants will absorb some of them, but only if there are sufficient other nutrients in the water (such as nitrates).
    2. Baking soda does not soften the water. It is sodium bicarbonate, and it does nothing to the calcium and magnesium.
    3. Water softeners are not suitable for fish tanks. All you can do is dilute the water with (safe) rainwater, or RO water.
    4. Fish urinate ammonia and phosphates.
    5. The conversion of ammonia to nitrate is a two-step process carried out by two groups of bacteria belonging to the genus Nitrosomonas and Nitrobacter. Neither of these bacteria can metabolize organic carbon to meet their energy requirements. Instead they derive their energy for growth from the oxidation of inorganic nitrogen compounds such as ammonia and nitrite. As a result of their unique metabolic pathways their growth rates are extremely slow and typical doubling times are in days compared to less than an hour for organisms that metabolise organic carbon. The slow growth rates of the nitrifying bacteria make them very sensitive to a wide range of physical and chemical parameters. Consequently a thorough understanding of the operational parameters and regular monitoring of the process is vital to ensure maximum nitrification is achieved.
    6. Ammonia is highly toxic. Lethal concentrations at a pH of 6.5 are 0.73 ppm, while at pH 8.5 only 0.17 ppm are considered lethal to inhabitants.
    7. Most fish can withstand ±40ppm of nitrate.
    8. You canÂt keep your fish in water that is toxic to them, yet you need to bring the nutrient level up as high as you can for your plants. This contradictory requirement gives you but one option:
    a. You still need to bring the ammonia level down as much as possible. (ie: by using a denitrification filter, but that means that you need to keep your tank sparkling clean. NO DIRT)
    b. You need to keep fish that are reasonable tolerant to high levels of nutrient. (ie: catfish, tilapia)
    c. You can only grow light feeding plants (ie: lettuce)
    d. You need to test the water regularly for ammonia, nitrite, nitrate and phosphate. You must do a water change whenever the levels overshoot the safety limits.

  • hinkson
    13 years ago

    I would just like to add to what greystoke said You need to urgently educate yourself on water chemistry.
    Firstly there is no water changeing in a balanced aquaponic system, meaning, You have to match the amount of plants(nute uptake) for the amount of fish(nute source)

    Cycling is nesseary because you are cultureing the bac. so that as soon as the fish produces waste it is converted to a form the the plants can use. You feed the fish - fishes waste feed the bac. - bac. waste feed the plants - You consume the plants. A good working system well have 0 or very low ammonia and nitrIte levels because it is constanly digesting/converting waste to food.

    I have had better luck with hard water than soft water in systems i build over the years. Hard water has pH buffering qualities. the harder the water the less your pH swings about. this helps to keep a system stable.

    The only filtration you need is a grow bed with a media that has a large surface area. to get a large enough bac. population for the job. cococoir is excelent. hydro cotton as well.

    In 20gall i would go for goldys, comets, mollies and a pleco(keeps the gravel clean). these fish are hardy and can handle the pH of 6to7 needed for aquaponics.

    By not cleaning the grow bed the nutes build up allowing you to grow any plant, not just leafy types as tought before. People used to think of aquaponics like hydroponics and used filters to remove solid waste, this is a nono. When these solids build up in the grow bed and brake down over time they provide enough nutes for fruit growth. I have grow carrots, peas, tomatos (love aqua) corn peppers pawpaw citrus................. all types off herbs

    Feed food high in protien = good nute source. (some use pre soke dog chow)you will allso have to suplement with iron chelate(wrong spelling?)no fish food has in enough for aqua. some sea shells are nice to add in the water because they have in TRACE amounts of MICRO nutes.

  • greystoke
    13 years ago

    Interesting to find a proponent of "dirty" aquaponics. That was a lively topic of discussion here in Africa a few years ago, as it was thought to be more appropriate technology than "clean" aquaponics.
    Although accepted as a working system, it is a bit out of favor now, because it is too expensive (electricity, fish food) and too complicated to be an advantage over keeping ordinary farm animals. ie: pigs, goats, chickens, etc. and feeding the waste to a veggie patch. The only benefit of "dirty" aquaponics is the fact that it is a closed system which prevents the loss of nutrients.

    For info: The Keyhole Garden has become very popular.

  • hinkson
    13 years ago

    I like the term 'dirty' aquaponics but i prefer 'pratical' aquaponics. Another benefit would be low water use.

    Being dependent on electricity, aquaponics is suited as a small backyard operation, for someone who wants to grow their own organic food.

    Then there is the 'food miles' you are saveing, meaning, the fuel, time and energy it takes to get that food on your table from the next side of the globe who knows........ Barbados

  • greystoke
    13 years ago

    hinkson wrote:
    Being dependent on electricity, aquaponics is suited as a small backyard operation, for someone who wants to grow their own organic food. Then there are the 'food miles' . . .

    I totally agree. I wasn't running you (or your system) down. My hobby (interest) is experimental hydroponics with the aim of introducing it in rural Africa.
    So far, hydroponics and aquaponics isn't making it compared to say The 'Keyhole' Garden.

  • hinkson
    13 years ago

    My next step is to take the system completely off the grid by useing a combantion of solar and wind power.

    I havent looked at keyhole gardens yet are they a type of hydroponics?

  • greystoke
    13 years ago

    It's not hydro. It's based on a central compost heap filled with kitchen and garden waste. The heap leaches its nutrients into a raised circular veggie patch surrounding the heap. You get to the heap via a foot path "slot" in the veggie circle. Hence the name "Keyhole Garden".

    It's a simple and effective method. Trouble is . . . one will do it, and others will steal it empty. Result . . no-one does anything.
    In a lot of these african communities any form of ownership is a liability.