How much nitrate is safe for fish?

Contrary to popular belief, nitrate is not good for fishes. Nitrate is the end product of fish wastes and is most frequently removed by performing water changes or by plants. So, it is a good idea to have some aquatic plants in your aquarium and to carry out regular partial water changes and rinsing of your filters.

How much is safe for your fish? This article suggests a nitrate level of <250ppm is needed for turbot.

Aquaculture
Volume 329, Number 2 (January 2012)
	The chronic effect of nitrate on production performance and health status of juvenile turbot (Psetta maxima)
	Authors:	Chris G.J. van Bussel, Jan P. Schroeder, Sven Wuertz, Carsten Schulz
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 329, Number 2 (January 2012)
	Page Numbers:	163 – 167
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	The chronic effect of nitrate on the production performance and health of marine cultured fish species is still unknown. Thus, the aim of the present research was to evaluate the chronic effect of nitrate on production parameters and health status of turbot (Psetta maxima). Juvenile turbot were exposed to 0mg/L NO3–N (control C), 125mg/L NO3–N (low nitrate LN), 250mg/L NO3–N (medium nitrate MN) and 500mg/L NO3–N (high nitrate HN) for 6weeks in small-scaled recirculating aquaculture systems (RAS). After 42d, biomass yield, length, weight and specific growth rate (SGR) were significantly (p<0.05) lower for LN, MN and HN compared to C. Mortality, food conversion ratio (FCR), condition factor (CF) and splenic index (SI) did not differ significantly (p0.05) between C and LN but were significantly (p<0.05) higher in the MN and HN groups. Hepatosomatic index (HSI), total hemoglobin (Hb) and methemoglobin (MetHb) did not show significant differences (p0.05) between treatments. Thus, nitrate negatively influences the production performance of turbot, even at low concentrations and nitrate management is therefore a key-factor in turbot RAS production.
	Citation:	Chris G.J. van Bussel, Jan P. Schroeder, Sven Wuertz, Carsten Schulz . The chronic effect of nitrate on production performance and health status of juvenile turbot (Psetta maxima). Aquaculture, Volume 329, Number 2 (January 2012), pp. 163-167, <http://ejournals.ebsco.com/direct.asp?ArticleID=412791CE5E21268B02DA&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=412791CE5E21268B02DA