Phosphate Test


Prolific Poster
Mar 26, 2006
Lexington, KY
I read somewhere about when looking for a P04 test kit that I do not want a kit that measures total phosphates but one that measures ortho phosphates.

Correct me if I am wrong please.

I purchased a Nutrafin P04 test kit but can't find anything on it about ortho compared to total phosphate. Can anybody tell me anything about this?

Also, my tape water measures 1.0 P04. My tank before water change was 5.0 P04 which is the max for this test kit. After a 50% water change it measures just over 2.5 P04. Should I still be dosing KH2P04?

I dose E.I. for 25 gallons water in a 29 gallon tank:
1/4 tsp KN03 3 X a week
1/8 tsp K2S04 3 X a week
1/16 tsp KH2P04 3 X a week
on off days:
1/8 tsp CSM+B 3 X a week
1/16 tsp FE (chalated) 3 X a week
Also on water change day I add 1/2 tsp Grumpy's GH booster for the added nutrients etc.

Mid week my paramters are:
P04 - 5.0
KH - 180
GH - 300
PH - 6.6 to 6.8 (mid day)
NH3 - 0
N02 - 0
N03 - 40

Tap Water:
PH 7.2
Nitrate according to the city's water report is .16
Phosphate according to the city's water report is 1.5

I have a heavy fish load and heavy plant load. Pressurized C02 @ 2 bps, Drop checker is green to yellow green. Lights, 130 watts CF, 6700k. I have good water circulation and surface movement. Water temp 76 degrees.

Can anybody examine and recommend anything on this?

Thank you so much.



Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Sacramento, CA
You have a small chance of having an accurate phosphate measurement using any test kit made for hobby use. If you use the EI dosing method, you don't need to know how much is in the water. You just "reset" the amount by doing the 50% water changes. Even if you are off and you actually have 10 ppm of phosphate when you do the change, and that isn't likely, you still aren't in trouble.


Lifetime Charter Member
Lifetime Member
Mar 21, 2005
Hi Joe,
I agree with hoppy. My recommendation is to throw away your PO4 test kit as well as your NO3 test kit. Yor ammonia and nitrite kist also have limited use. It's very doubtful that you have zero ammonia or zero nitite. The zero reading simply means that the reagents are not capable of reacting to concentrations below a certain value, that's all. The job of those two kits is to advise you if the ammonia/nitrie levels are toxic to fauna. They cannot measure below toxic levels.

Any tank with living things in it has ammonia and nitite. The nitrifying bacteria depend on the existence of these waste products so it is not possible that the values are zero, otherwise the bacteria would die.

EI ensures that you have at least enough of everything so there is no need to measure these values at all. Take the money you save from not buying these kits and buy more plants instead. Use the time you save by not having to do all those flawed tests to relax, have a beer and to enjoy looking at your tank.


Tom Barr

Staff member
Jan 23, 2005
You may use the test kits, but they do need calibrated to ensure accuracy, otherwise you have little confidence that they are accurate and telling you "the truth".

This is a more complicated process and you need a decent scale and the chemicals and a way to measure liquids accuracy etc.

A lot more to learn and do:p
the problem in the hobby, one I've stated going back a de cade or more now, is that folks do not bother, they assume, like most hobbyists do, that the test kits are accurate to begin with, they are not.

I thought so years ago.
Advice says test, so I did.
I had little notion that the test kits might not be accurate.

It's a wake up call to some degree.

Tom Barr


Prolific Poster
Mar 26, 2006
Lexington, KY
Thanks Tom and everybody else.

I know the test kits are not real true. I use them to spot any hikes or major changes. I'm not sure how to calibrate them. I wasn't much of a brain in science class.

I, like some others, try to figure out the little things with my limited knowledge, how to fix the little things that many people just don't worry about. Trying to get a very prestine tank. One that is worthy of submitting in one of the best tank compotitions. Everyone that see's my tank says how great it looks but I see little things that I would like to see better. I guess I am a perfectionist which sometimes is a problem for me because I keep trying to make it better. I get it just right and then a couple days I see something that needs attention or change. LOL