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View Full Version : PO4 and TDS .... another view


JB63
02/03/2010, 07:14 PM
There has been a lot of talk on using additional filtering (e.g DI) to lower Phosphates. It is implied that a high TDS is always cause for high Phosphates.

Well, I took a shortcut. I have a 3 stage RO only, no DI. I simply measured PO4 in my freshly mixed water and the reading was zero. Thus, PO4 in my tank is because of feeding and nothing else. If it's only for PO4, no need for me to invest in a DI unit ....

Where's the flaw in this argument?

JB63
02/03/2010, 07:17 PM
Mod, please delete. I clicked twice on the 'submit' button.

Thanks.

Randy Holmes-Farley
02/04/2010, 08:37 AM
The purpose of a DI is, IMO, much broader than phosphate.

Copper, ammonia, silicate, etc are all concerns in tap water, and ammonia and silicate, for example get through an RO pretty well. If your water supply uses chloramine, there will be a lot of ammonia in the RO effluent, so you might check that at least. :)

I discuss what each part of an RO/DI accomplished here:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm



It is implied that a high TDS is always cause for high Phosphates.

Actually, I think careful investigations show top off water to not be the usual primary cause. A little fish food always has a lot of phosphate, and elevated tank phosphate is always just a matter of not having enough export to balance the imports, which can include tap water, but nearly always includes a lot from fish foods.

I discuss sources and export methods here:

Phosphate and the Reef Aquarium
http://reefkeeping.com/issues/2006-09/rhf/index.php


The “How To” Guide to Reef Aquarium Chemistry for Beginners,
Part 4: What Chemicals May Detrimentally Accumulate
http://reefkeeping.com/issues/2007-09/rhf/index.php