I would suggest that the levels of nutrients (phosphate and nitrate), relative to each other, are more important than keeping either one at at a specific target level (up to a point, of course). As each tank is inherently different, one person's ratio may be somewhat different to anothers and the reef keeper must find what works best for his/her own system.
This is a great read and looks at this subject on wild reefs, but much is applicable to corals in a captive environment: Impacts of nutrient enrichment on coral reefs: new perspectives and implications for coastal management and reef survival.
I like this excerpt since it illuminates the fact that nitrogen and phosphate limitations can be different for various reef locations, as well as seasonal.
'Defining nutrient concentrations or nutrient ratios that represent thresholds for the different direct and indirect nutrient effects on coral reefs and to introduce optimised target values that promote reef resilience are important tasks for nutrient biology research. When assessing the impact of nutrient enrichment on coral physiology in the field, it should be considered that some effects could be subtle and might become detectable only after longterm exposure or under distinct circumstances, for example, during periods of stress. Importantly, many effects may vary locally depending on the regional reef water biogeochemistry. In the Great Barrier Reef, for instance, many processes are nitrogen-limited [69•], whereas phosphorus availability seems to be limiting in other sites such as Discovery Bay, Jamaica [52]. The data reported by Lugomela et al. [ 83•] suggest that in yet another case, the East African waters, nutrient limitation might switch seasonally between nitrogen and phosphorus. Accordingly, the effects of nutrients on different coral reef ecosystems may vary significantly and need to be assessed individually.'
This is a great read and looks at this subject on wild reefs, but much is applicable to corals in a captive environment: Impacts of nutrient enrichment on coral reefs: new perspectives and implications for coastal management and reef survival.
I like this excerpt since it illuminates the fact that nitrogen and phosphate limitations can be different for various reef locations, as well as seasonal.
'Defining nutrient concentrations or nutrient ratios that represent thresholds for the different direct and indirect nutrient effects on coral reefs and to introduce optimised target values that promote reef resilience are important tasks for nutrient biology research. When assessing the impact of nutrient enrichment on coral physiology in the field, it should be considered that some effects could be subtle and might become detectable only after longterm exposure or under distinct circumstances, for example, during periods of stress. Importantly, many effects may vary locally depending on the regional reef water biogeochemistry. In the Great Barrier Reef, for instance, many processes are nitrogen-limited [69•], whereas phosphorus availability seems to be limiting in other sites such as Discovery Bay, Jamaica [52]. The data reported by Lugomela et al. [ 83•] suggest that in yet another case, the East African waters, nutrient limitation might switch seasonally between nitrogen and phosphorus. Accordingly, the effects of nutrients on different coral reef ecosystems may vary significantly and need to be assessed individually.'
