Hi all,
In the marine tank world PO4 testing is "quite important" and some reefers run posphate removers or reactors depending on if they need to add/remove it. They're very fussy about it and bang on about getting the levels just right. So the question is. Are the marine PO4 test kits different from the freshwater ones ie: are they more accurate/more reliable or are they still just as useless as freshwater ones (bearing in mind the salifert ones are really really expensive too !)
Depends upon the test kits, you can get semi-quantitative colormetric kits that will accurately measure PO4--- levels down to single figure values, but I would be dubious that they will give accurate levels below about 5ppm. Hanna do an electronic meter, the HI-83203-02 that might give you more accurate readings for about £400 + reagent costs.
What you have to remember is that the situation is different in reef aquaria, where marine "plants" (Green (Chlorophyta) and Brown algae (Phaeophyta)) are unwanted, and Red algae (Rhodophyta) may be desirable if they are coralline algae, but often undesirable if they are foliose forms. You also have a lot of symbiotic relationships where the zooxanthellae in Cnidaria are frequently diatoms etc. These organisms have evolved in very low phosphate environments and are very adapt at scavenging minute amounts from their environment, realistically an aquarium with "no PO4---" will always have enough phosphorus available for it to be non-limiting. You also have the issue that large scale water changes are more difficult in marine aquaria, mainly because of the cost and availability of salt water.
If we ignore test kits and work on the premise that we want to remove PO4--- all together, it becomes a lot easier, because the majority of phosphorus compounds (with calcium (Ca), iron (Fe) etc) are insoluble. Phosphate stripping, (using ferrous ammonium sulphate heptahydrate ((NH4)2Fe(SO4)2·6H2O) as a precipitant), is widely used in the waste water industry and is very effective removing about 95% of the phosphate, or you can use a FeOH3 based phosphate remover like "Ultiphos" or "Phosban" etc in a phosphate reactor. Because you can't really test when the "Ultiphos" etc. is exhausted (back to the test kit problem), the easiest option is to keep on replacing it on a regular basis well before it is all reacted.
I had quite a long discussion with the seller of "Ultiphos" on the BCA forum, it does get a bit chemistry orientated, but it covers this area in some detail. <
http://www.britishcichlid.org.uk/phpBB3/viewtopic.php?f=57&t=7161&hilit=iron+phosphate>
Personally I think most marine aquarists would be better of combining the reactor with an algal scrubber, or even better with a refugium with higher plants like Eel Grass
Zostera and Red Mangrove
Rhizophora mangle, but for a lot of them my suspicion is that it is the high tech. expensive "shiny toys" they like.
cheers Darrel