Aquaponics FL

Inputs ยท what you add, and why

What you add to an aquaponics system

Fish feed runs the system, but a few things have to be added by hand: bacteria to start it, iron and potassium the plants run short of, calcium and buffers to hold pH, and the odd dose of salt. 12 inputs explained, each with its sources.

Starting a system

  • Cycling a new system (fishless cycling): A new system has no nitrifying bacteria yet, so the ammonia that fish give off has nowhere to go. Cycling means growing those bacteria before the fish arrive: one group turns ammonia into nitrite, a second turns nitrite into nitrate, which is what plants feed on. Feeding the young colony a measured ammonia source spares fish weeks of toxic water. Plan on about 3 to 6 weeks, and longer in cool water.
  • Starter bacteria (nitrifying bacteria cultures): Bottled nitrifying bacteria are sold as dry powders or concentrated liquids to speed up the start of a new biofilter. The sources treat them as a product class that is optional: a culture can shorten cycling, but a freshwater system will cycle without one, and media from a working system is the most effective seed of all.

Nutrients and supplements

  • Calcium: Calcium is usually short in aquaponic water, and lettuce tip burn and tomato blossom-end rot are the classic signs. Like potassium, it goes in as a base, either calcium hydroxide (fast) or calcium carbonate (slow), so it also offsets the acid from nitrification. In much of Florida, hard well water brings some calcium in with every top-up.
  • Chelated iron: Iron is the nutrient aquaponic systems run short of most often, because fish feed carries far less than vegetables need. It is added as a chelate: iron bound to an organic molecule that keeps it dissolved, since plain iron drops out of solution at the near-neutral pH aquaponics runs at. Most sources aim for about 2 mg/L.
  • Magnesium: Magnesium sits at the centre of the chlorophyll molecule, so a shortage shows as yellowing leaves. The sources disagree on how often aquaponic systems run short: FAO says adding it is generally unnecessary, while SRAC 454 says it may be limiting in some systems. Where it is needed, the documented way to add it is dolomite used as a pH buffer.
  • Potassium: Potassium is one of three nutrients (with calcium and iron) that fish feed does not supply in the amounts vegetables need. The sources add it in a form that also raises pH, so one addition both feeds the plants and counters the acid that nitrification makes. Fruiting crops such as tomatoes and peppers need it most.
  • Seaweed or kelp extract: Seaweed is the one organic supplement the FAO aquaponics manual names as rich in potassium and iron, the two nutrients aquaponic systems most often lack, and it recommends a home-brewed seaweed tea. Bottled kelp and seaweed extracts are popular with aquaponic growers, but we found no UF/IFAS, SRAC, FAO or extension document that tests or recommends them; their iron and potassium claims come from sellers.

pH

  • pH adjusters (acids, bases and buffers): Aquaponic water drifts acid on its own, because the bacteria that turn ammonia into nitrate release acid. So most systems need a base now and then, and the sources say to use potassium or calcium bases, which feed the plants at the same time. Acid is needed only where the top-up water is very hard and alkaline, which describes much Florida well water, and it has to be added with great care.

Water

  • Aeration and dissolved oxygen: Dissolved oxygen is the water quality factor that kills fastest: fish can die within hours, sometimes minutes, when it runs out. Fish, plant roots and the biofilter bacteria all draw on it, and warm water holds less of it, which makes Florida summers the risky season. Run air pumps all the time, add more in hot weather, and have a backup for power cuts.
  • Dechlorinating tap water (chlorine and chloramine): City water is disinfected with chlorine or chloramine, and both kill fish, plants and the biofilter bacteria. Plain chlorine gasses off if water stands and is aerated for a day or two. Chloramine, which several Florida utilities use, does not, and has to be removed with a chloramine-rated conditioner or an activated carbon filter.
  • Source water in Florida: well, rain and city water: An aquaponic system loses 1 to 3 percent of its water a day and has to be topped up, so the water you add slowly sets the system's chemistry. In Florida that usually means one of three things: hard, alkaline well water from the limestone aquifer; city water treated with chlorine or chloramine; or soft rainwater. Each works with the right handling; pond and surface water should be avoided.

Fish health

  • Salt (sodium chloride) for fish health: Salt is a cheap, widely used fish treatment, sometimes called the aspirin of aquaculture, for external parasites and handling stress. In aquaponics it belongs in a separate hospital tank, not in the system: the sodium harms plants, and sudden salt changes set back the biofilter.

Buying them in Florida

The supplies page lists Florida businesses that sell systems, media, nutrients and test kits, each checked on its own site. Most inputs ship fine; fish and plants do not.