# Phosfate (PO4) readings fluctuates



## winzdk (17 Jan 2021)

I've read that plants need some amount of PO4 for better co2 uptake, so I checked the amount 5 days ago and it was pretty much 0. Two days later I dosed PO4 (following the directions of 5ml per 100L = 13ml - I have a 360L tank, with a lot of hardscape and soil). 4 hours later I checked the readings and it was off the scale with at least >2.0 (I didn't try a diluted test). As too much PO4 is food for algea, I did a 20% WC a couple of hours after that.
Today, 2 days later, the reading is 0,2 (hard to tell between 0,1 and 0,3), which is the number I'm going for as it would be optimal for the plant's co2 uptake.

Can someone explain the "behaviour" of PO4 and how it relates to the rest of the chemistry, just in basics terms if possible  ?


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## ceg4048 (3 Feb 2021)

Hello,
        Instead of looking for explanations on the behaviour of PO4 you should instead investigate the behaviour of PO4 test kits, which are completely unreliable.

My advice is to dose your nutrients according to some pre-determined schedule and stop using test kits to determine nutrient levels, because you will only cause more trouble for yourself.

Cheers,


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