Inputs · Water
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.1, 2, 5, 6
Why you need it1, 2, 3, 7
The UF/IFAS curriculum sheet FA171 says even the slightest trace of chlorine can kill fish, that almost all US public water systems use chlorine, and that many add ammonia as a second disinfectant, forming chloramine, which is very toxic to fish. FAO says chlorine and chloramine are toxic to fish, plants and bacteria alike. SRAC 454 says municipal water should not be used in an aquaponic system unless it is dechlorinated, and SRAC 4502 says a new system's water must be free of residual chlorine before bacteria are added.
How to use it1, 2, 4, 5
1. Find out which disinfectant your water has. Ask the utility, or test: FA171 uses a chlorine test strip plus an ammonia test strip, since chloramine water shows both chlorine and ammonia. 2. Chlorine only: let the water stand with vigorous aeration. FA171's class test aerates for 24 hours and re-tests, waiting another 24 if any chlorine remains; FAO says it can take upwards of 48 hours, faster with air stones; the UF/IFAS guide HS1252 says to aerate city water in a separate tank for a few days and test it before it touches fish. Sodium thiosulfate neutralises chlorine at once (FA171). 3. Chloramine: aeration alone is not enough; FA171 found chlorine falls but probably not to zero, and ammonia stays. Use a conditioner made to remove chloramines or a granular activated carbon filter (Pinellas County; FAO also names charcoal filtration and dechlorinating chemicals). FA171 notes sodium thiosulfate clears the chlorine part, while zeolite or a combined chlorine, chloramine and ammonia neutraliser deals with the ammonia. 4. Top up in small amounts: FAO's rule is never to replace more than 10 percent of system water without first testing for and removing chlorine.
In Florida6, 5
Tampa's Water Department says it mainly disinfects with chloramine and switches to plain chlorine several times a year, usually in winter and summer, for three weeks at a time, and that aquarium and pond owners should already be removing both. Pinellas County changed from chlorine to chloramine in 2002, after its supplier Tampa Bay Water began blending groundwater, surface water and desalinated water; it says chloramines must be removed from water for fish tanks and ponds, will not evaporate the way chlorine does, and release ammonia when removed chemically. Check with your own utility: these two are examples, not the whole state.
Cautions5, 1, 3
Removing chloramine chemically frees ammonia (Pinellas County), which is itself toxic to fish; Pinellas says biological filters, natural zeolites and pH control reduce its effect, and a cycled aquaponic biofilter is a biological filter. Do not assume water left to stand is safe if it is chloraminated (FA171, Pinellas). Never use pond or other surface water as a substitute; SRAC 454 says it may carry disease organisms.
What to buy5, 1
Read the label for the word chloramine: Pinellas County says to use a conditioner designed to remove chloramines, or a granular activated carbon filter, and to ask a pet supplier. A product that only claims to remove chlorine (for example plain sodium thiosulfate) will leave chloramine's ammonia behind (FA171). Chlorine and ammonia test strips let you check the result (FA171).
What this page doesn't cover yet
- No statewide list of which Florida utilities use chloramine was found; only Tampa and Pinellas County pages were read. Other utility pages (for example Fort Lauderdale, Palm Bay) appeared in search results but were not opened.
- FAO says off-gassing is usually enough for small units even on chloraminated water, which conflicts with FA171 and Pinellas County; the page follows the Florida and UF/IFAS sources.
- No source gives a dose for sodium thiosulfate or carbon filter sizing for a home system. FA171's teacher table gives product coverage figures tied to named catalogue items, left out here.
- FA171 names specific products and a supplier catalogue; brand names are left out per the schema rule.