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Re: Basic planted tank question

Conlin and Sears (and others) advocate keeping phosphate concentration very 
low (much less than 0.1 ppm)as an aid to keeping algae under control. The PMDD 
approach is designed to do this by supplementing with nitrate to force 
nitrate, rather than phosphate, to become limited. 
	If your tank really has 2-4 ppm phosphate, as you reported, that is 
exceedingly high and would be predicted to invite algae problems. Since your 
nitrate concentration seems to be low (<5 mg/ltr), you must be adding 
phosphate somehow. Have you tested your tap water (assuming this is what you 
are adding at water changes)? Some tap water does contain substantial 
phosphate. If this is the source, you will probably have to treat the water in 
some way to reduce the phosphate, either with a phosphate-binding resin 
(Phosph-Zorb, or some such product), or use a deionizing or RO system and 
reconstitute the treated water with appropriate salts.
	Before doing anything, check that phosphate reading to be sure it is 

	Concerning intentional addition of phosphate, very few recommend it, 
except in very specific situations. 

Rick Denney, Dickinson, TX
rdenney at ibm_net