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PO4 from tapwater..?

Cor

Cor

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Joined
3 Nov 2015
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389
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The Netherlands
lets say; I want to mix my own EI solutions and I like to have 20ppm PO3 in the water

I have measured the tap water and it contains about 2 ppm PO4. That would be nice in proportion to the KNO3 (10:1 ratio) Could this mean that I don't need to add PO4 because it is already in my tap water? This would be supplied by the weekly water change. Does it makes sense?

tia Cor
 
Cor said:
I want to mix my own EI solutions and I like to have 20ppm PO3 in the water
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You mean NO3, right?

Cor said:
I have measured the tap water and it contains about 2 ppm PO4. That would be nice in proportion to the KNO3 (10:1 ratio) Could this mean that I don't need to add PO4 because it is already in my tap water? This would be supplied by the weekly water change. Does it makes sense?
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Remember, plants consume PO4 and you would have 2ppm after a water change only if you changed 100% of the tank water... if you change 50%, you're adding only 1ppm to your tank (assuming it had gone down to 0ppm during the previous week).
 
EI ranges are for 20-30ppm of NO3 not N the Nitrogen out of NO3 is actually lower. P and PO4 is at 3-9 PO4. I think PO4 and P are different I.E if you add 9ppm of PO4 you only actually add 3ppm of Phosphate. Depends what you measured so if you measured for PO4 and it was 2ppm out the tap apart from the test kit not being that accurate the actual phosphate value will be lower. I recently discussed this with my local water authority who confirmed that they do indeed tend to add 2ppm of po4 to tapwater because firstly it coats pipework to prevent corrosion and stop lead from old pipe work leaching into the water and secondly they add it because it reacts with heavy metals like Iron and precipitates out so they can filter it out of the water supply. That's why with EI we don't mix PO4 and traces in the same bottle and dose them on separate days. If you do the water can go cloudy and this is how the water board filter it out using fine micron filters.

If it was me because I'm in the same boat I would just ignore the fact that there's PO4 out of my tap as a 50% WC won't be adding enough to last a week if you have co2 and med/high lighting anyway I would just look at it that there is some in the tap, the fish food will also add some so if you wanted to not add as much you could start at full value and gradually reduce it in your bottles to you see any issues with your plants.

Also bare in mind with the PO4 salt you also add Pottasium so emitting it from your EI mix will leave you low on K (pottasium) as well although this is not as important as the other macros in the big scheme of things.
 
Most people who decide roll their own ferts mix (this is NOT EI of course), because they are under the false assumption that they can use the ferts supplied in their water, "cos their test kits says so" always end up in trouble.

So any saving in salts dosing PO4 salt and MgSO4 (more usually people omit MgSO4 "cos their water is hard" ) is more than blown away by the fact that their plants die and very quickly get covered in algae.

So in summary, KH2PO4 and MgSO4 are cheap, so just dose EI, one less thing to waste worries about and get on growing plants not algae.

Excess NO3 and PO4 or even Mg from the water will in the end make no difference. More than likely they are not present in tap water, or present in low levels, but if using a hobby grade test kit will indicate presence in high levels due to interference issue in using cheap kits.
 
like @ian_m says best just ignored. If it makes you feel better a long while back using an API test kit I had my tapwater was measuring somewhere in between 5-10ppm depending on which angle I was looking at it with sunlight. When I asked the water board for a reading because they don't have to publicly release this information with it not being toxic in any way, shape or form they said the average PO4 values for 2016 were 0.96ppm. They then went on to say in general as a max they would generally add 2ppm and that goes for most UK water authorities. When I asked about the 5ppm the said "Oh no, we would never put anywhere near as much as that in". So from that you can see that even in the unlikely even even that they did put 5ppm in which isn't very likely with a 50% WC that would still on add 2.5ppm or 1 of your 3 per week doses so you're still shy of 2 more doses. Because the average was 0.96ppm and their max was 2ppm that also tells you they don't add the same amount all the time so you have nothing to work off if they change. At least with you adding the whole of the ferts you know exactly what you're getting and as Ian said more is better than less. Less can equal problems where more doesn't so best to play it safe.

The world health organisation has set 5ppm in tap water to be the absolute max but not for health reasons. It's mainly because Phosphate when released into rivers DOES cause algae which is where a lot of the confusion of algae and phosphate come from. But this isn't the alga alone, the increased PO4 causes plants in the river to accelerate growth and dead leaves fall off the plants decomposing on the river bed at a faster rate than the natural river system can break it down causing low oxygen and increased algae competing for oxygen further. This reduces the life of the system from thousands of years and the system collapses.

To look at it another way if they did have 5ppm you would barely have a days dose and at both 0.96ppm or 2ppm which is more realistic it isn't worth even thinking about or taken into consideration in your dosing regime.
 
True, obviously there's nothing to say that you need all that po4 that's basically what EI is. It doesn't tell you how much you will need it tells you how much you won't. It just says that adding anymore than that combined with a clean tank, good co2 levels and good circulation would be pointless and a waste of fertiliser. If you want to see how much less, you could add slightly less weekly but you really need to know your plants and know when they are missing the PO4.
PO4 test kits aren't really the way to do it, I've been there so I'm talking from experience, it does on face value appear to be the answer if the tests were accurate enough and I and probably others wish they were.
I think I first tried with a hagen test which only went up to 1ppm so you can guess my reaction when I saw it was right off the scale! Fair enough in Marine or fish only systems where any po4 is probably not good and is probably what they are more designed for but in a planted system where we are dosing po4 it's sort of like testing for something that you already know fine well is in there because you've just put it in and in most cases will need it.
As for trying to find the difference between 0.5 and 1.0ppm as the hagen kits do its not even like looking for a needle in a haystack it's like looking for two :)
 
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