Inputs · Starting a system
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.1, 2
They answer the slow start of a new system. Nitrifying bacteria need 10 to 15 hours to double in number (FAO), so a colony built from the few cells that arrive on their own takes weeks. SRAC 4502 says prepared cultures are not essential but can shorten the time it takes to establish a biofilter. The UF/IFAS start-up plan in HS1252 adds a culture on day 4, alongside a household ammonia dose, which it says gives a quicker start and lets plants go in early.
Prepare the water first: no chlorine left in it, at the running temperature, with pH and alkalinity set, and with an ammonia source in place (SRAC 4502, steps 1 to 4). Then add the culture as the maker directs; SRAC 4502 notes directions may call for adding it in several portions and for feeding it the nutrients supplied with it on a schedule. SRAC 452 describes pre-activating a biofilter for 2 weeks before stocking by seeding it with a commercial culture and giving it a growth medium of ammonia, trace elements and a buffer. Whatever you add, keep testing ammonia and nitrite as described under Cycling a new system: the product seeds the colony, it still has to grow.
Chlorine and chloramine kill nitrifying bacteria, so start-up water must be free of residual chlorine (SRAC 4502). Tampa's water department uses chloramine most of the year and Pinellas County has used it since 2002, and neither gasses off the way plain chlorine does; treat city water for chloramine before adding a culture (see Dechlorinating tap water).
Bacteria brought in from any outside source can carry disease organisms with them; SRAC 4502 says to weigh the method against your biosecurity plan. Chlorine, bleach residues and fish treatments such as formalin, copper sulfate, potassium permanganate and some antibiotics kill or inhibit nitrifiers (SRAC 4502, SRAC 452). In moving-bed or mixed-bed filters, strong aeration can scrape new bacteria off the media; SRAC 4502 suggests reducing agitation until ammonia and nitrite start falling, then raising it again. SRAC 4502 also reports that cultures are essential when starting brackish or marine systems (above 15 ppt salinity), which a freshwater aquaponic system is not.
Match the product to the water: cultures are sold for freshwater and for marine use, and nitrifying bacteria species differ in the salinity they thrive in (SRAC 4502). Note the form (dry powder, liquid suspension or chilled live culture) and follow the storage and shipping directions (SRAC 4502). FAO warns these products can be expensive or hard to find and calls them ultimately unnecessary; its alternative is a share of biofilter media from another aquaponic system, which it says greatly shortens cycling, and SRAC 4502 also names moved biomedia as the most effective seed (with the disease caveat above). No source rates brands.
Restated in our own words from these documents, written 2026-11-02. Doses are the sources' figures; test your water before and after.