Phosphate reading too high

eddtango

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May 20, 2005
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My Tank is 75 gallons. I've been dosing 3 x / week 1 tsp KNO3, 3/8 tsp K2SO4 and 1/4 tsp KH2PO4 and 2 tsp of Equilibrium. On alternate days,I dose 10 ml Seachem Flourish. My nitrate reading is 5ppm but my Phosphate is 10 ppm. I might have overdose on the phospate.
 

VaughnH

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First of all, since you are using your phosphate test kit to determine how much phosphate is in the water for dosing purposes, you need to calibrate the test kit. It could be way, way off. You need to mix a known ppm of phosphate in some DI or distilled water, use the test kit measure the ppm and compare the readings. Make sure you bracket the readings you want to achieve with a couple of calibration points. Phosphate test kits are not known to be very accurate in the ranges of interest to us.
 

eddtango

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May 20, 2005
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VaughnH;14789 said:
First of all, since you are using your phosphate test kit to determine how much phosphate is in the water for dosing purposes, you need to calibrate the test kit. It could be way, way off. You need to mix a known ppm of phosphate in some DI or distilled water, use the test kit measure the ppm and compare the readings. Make sure you bracket the readings you want to achieve with a couple of calibration points. Phosphate test kits are not known to be very accurate in the ranges of interest to us.

I'm using Aquarium Pharmaceuticals Phosphate test kit. I tried testing a newly setup 10 gal bare bottom tank and it tested very minimal Phosphate reading compared to the the tank that had some dosage of KH2PO4.
How many percent of original water is to be mixed w/ DI water for testing?
 

Tom Barr

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Sounds like a bad test kit to me.
Do a large water change on the tank and take before and after measurements also.


Regards,
Tom Barr
 

eddtango

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Tom Barr;14801 said:
Sounds like a bad test kit to me.
Do a large water change on the tank and take before and after measurements also.


Regards,
Tom Barr

Will the high PO4 reading affect my Discus? Right now,their fins are clamped and shut,they also became darker. All 6 fish have started to huddle in one corner of the tank. The SAEs seem not to mind it. I also performed a 50% water change but to my surprise,the reading is still 10ppm.
Maybe, I should do another 50% H2O change.
 

Tom Barr

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Did you try adding some KH2PO4 to a glass/bucket of DI water and test?
Take 10% of that and dilute again with DI water.
Measure.

You should get 1/10th the previous reading.
If not, toss the test kit.

Discus like large massive water changes, that's what every breeder does.
Many do 50% 2x a week.

Discus buffer by SeaChem and other pH lowering chemicals have various PO4 buffers in them and these can form a non carbonate alkalinity. That's how theyn target a pH of 5.8 without CO2 and why it messes with CO23 at high levels if you use the tank's KH reading. It gives a false positive CO2 reading, you think there's more CO2 than is really there.

Peat/ADA AS/some soils do the same thing.
Tap waters can have high PO4 they sometimes add it for corrosion control.

Regards,
Tom Barr