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Re: adding PO4 & Fe

Jay Reeves <jbreeves at isd_net> wrotw:
> Subject: adding PO4 & Fe

> Does KH2PO4 = potassium phosphate? and what is H3PO4?
> I have a small jar of Sodium Phosphate, Tribasic can this be used to add
> P?
> Also have a LaMotte PO4 test kit to manage additions.  Could someone
> offer some guideline to how to mix and dose PO4?  i.e. 1t KH2PO4 + X amt
> water then dose about X ml per X gal.  I have been a very happy camper
> since quitting the RO scene :-) thanks Tom and all!  Plants really perk
> up after a water change now.  Tap has 0.2 PO4 and I do a 50% water
> change.  After water change PO4 is undetectable within 24 hrs. (probably
> less).  

KH2PO4 = potassium phosphate, monobasic.
K2HPO4 = potassium phosphate, dibasic
K3PO4, or K3PO4 - H2O = patassium phosphate, tribasic

Check out the link about H3PO4, which is phosphoric acid. We 
went through this last month. There's lots of replies to the initial 


Yes, you can use sodium phosphate, but be aware; sodium 
phosphate is Na3PO4 - 12H2O (dodecahydrate) mw 379.9 (25.00% 
PO4). It's got lots of Na and water, and PO4 is what you're after. 
Also, a 1% solution is pH 11.8-12.0, store out-of -reach. To figure 
out how much to use and how much to dose, go to the chemistry 
section of my website and run through the formulas; it's a lot easier 
than requoting everything.


Heck, just change the water often and get free PO4!<g>

> another dosing question - how much TMG to add to a 75gal? 
> KH from the tap is 2 - raised to 5 with baking soda.  Have been trying
> to keep the nitrate close to 10 but forget or neglect for 1 - 2 days and
> it goes to <2.   I had been following the suggested TMG dosage of about
> 10 - 15 ml / week for my size tank / water hardness.  Using a LaMotte FE
> test kit readings were always well below 0.10.  Recently have increased
> dosage to as much as 45 ml / week.  Is this excessive?  Readings are
> still within reason <0.10 and the plants are looking much better.  

The bottle states 5ml / 50L, which is 5ml per 13.2 gals, or in your 
case, 28.4 mls for 75 gals (water column). Probably a little less 
depending on how much water is in your column. Your 10-15 mls / 
week probably wasn't enough. 45ml may be excessive. The bottle 
also states that soft water folks should use less, anyway. 

Also, you said you missed a couple of days of dosing what, 
KNO3?, and your nitrates fell to zero. TMG doesn't contain NO3 or 
PO4. Hopefully that wasn't what you were referring to ;-). 

Jamie    <"\\\>< Aquatic plants, water chemistry, and cichlids
Greenwood, SC     http://www.ais-gwd.com/~jjirons