# potassium and phosphate levels for Bournemouth water



## NatureBoy (23 Aug 2013)

(a bit of background...)
I inherited an API nitrate test kit about a year ago. A few weeks ago I decided to test the test kit and was surprised that after following the instructions to shake the bottle like a maniac for 30 seconds I got a colour reading that tallied with the water company of about 20ppm (From the water quality report, nitrates are on average 22ppm). This was the first time that I've seen a correlation between test kit and water company. With a bit of extra confidence I then decided to test the aquarium water and was really surprised to see the nitrates were somewhere like 60ppm...a colour reading like irn bru. This in itself was not a concern but definitely not what I expected, I was thinking they'd be much lower and forced me to rethink my understanding of what was going on. Since then I've definitely changed tack with my fert regime. I've stopped routinely adding nitrates on the assumption that they were limited. I'm doing week / twice weekly 25% water changes to bring the nitrates down in line with the tapwater 20ppm.

(back to the thread)
Now I'm using tap water as a routine way of adding nutrients to the water column I was keen to find out what the levels for potassium and phosphates were (these aren't stated on the water quality report)
With time on my hands I contacted Sembcorp and was told on average *Potassium is 2.42 ppm*, *Phosphates are an insignificant 100 micro grams per liter*.

I know we shouldn't expect much phosphate in the water column due to it binding to substrates.  I'm guessing my water column, and as such the moss and ferns, are at first phosphate deprived following a water change yet with unlimited nitrogen. I've just made a potassium phosphate solution and added enough to raise whatever phosphate level by 0.5ppm to see what effect this has. (I know some would say whack in more, but softly, softly...)

Not really sure what the point of this post is, other than a reminder to myself about what I'm doing!


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## roadmaster (23 Aug 2013)

Last time I tested for nitrates in 80 gal low tech, with weekly 1/2 tsp of KNO3, reading was near 80 ppm.
This was a couple year's ago before I understood completely the difference between nitrates as result of food,waste,and nitrate reading's from dry mineral salt's.
Have since binned the test kit's for my plant's,shrimp's,fishes,are all doing well.(these are much better gauge ,more fun to look at).
I also add phosphates at same 1/2 tsp each week,and only a little brush algae on wood pieces rather than the promised deluge of algae that i alway's believed would be the result.


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## dw1305 (23 Aug 2013)

Hi all,


NatureBoy said:


> I got a colour reading that tallied with the water company of about 20ppm (From the water quality report, nitrates are on average 22ppm). This was the first time that I've seen a correlation between test kit and water company. With a bit of extra confidence I then decided to test the aquarium water and was really surprised to see the nitrates were somewhere like 60ppm.......This in itself was not a concern but definitely not what I expected, I was thinking they'd be much lower and forced me to rethink my understanding of what was going on.


 I think you have to be really careful interpreting the results of the nitrate test kit in your tank water. The problem with most forms of anion analysis is that you get interference from other anions.

In the tank water you have added other salts (say MgSO4.7H2O), because you want the Mg++ ions, but you also get the "unwanted" SO4-- ions. There is much more about this in this thread: <Mg+K+Fe=no NO3??? | UK Aquatic Plant Society>.

If you want to dose EI, I'd stick to the recommended dosing.

If you don't want to dose EI, you can always use an alternative method of dosing, that isn't reliant on testing. I like the "Duckweed Index", where you use the colour and growth rate of floating plants (floating plants have access to aerial CO2, so CO2 shortage is not part of the equation) as a proxy for the nutrient status of the tank.

Have a look at: <Water Lettuce and it's impact on my tank | UK Aquatic Plant Society> & <Osmocote with soil, soil retainer? | UK Aquatic Plant Society>.

cheers Darrel


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## NatureBoy (23 Aug 2013)

dw1305 said:


> Hi all,
> I think you have to be really careful interpreting the results of the nitrate test kit in your tank water. The problem with most forms of anion analysis is that you get interference from other anions.
> 
> In the tank water you have added other salts (say MgSO4.7H2O), because you want the Mg++ ions, but you also get the "unwanted" SO4-- ions. There is much more about this in this thread: <Mg+K+Fe=no NO3??? | UK Aquatic Plant Society>.
> ...


 
Hi Darrel

I don't add sulphates directly, any magnesium I have been adding is via magnesium nitrate. I take on board the general concern about accuracy and read the threads, so this is mainly to furnish understanding of what is going on. What other anions would be kicking about in such quantities  to affect readings?

Also just on a like for like comparison, if tapwater registers a light orange and aquarium water a very dark "irn bru" orange, and that the source of all aquarium water is from that tap water and I have not added more sulphates, can I not roughly conclude I have more nitrate in the aquarium water?

ps all the nitrate business aside, adding a splash more potassium phosphate has allowed the fissidens to get happy and is creating oxygen bubbles, suggesting there was a phosphate / potassium limit kicking in a day or two after water change.

cheers


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## dw1305 (23 Aug 2013)

Hi all,


NatureBoy said:


> What other anions would be kicking about in such quantities to affect readings?


Any really, the main one for interference is the chloride ion, Cl-.


NatureBoy said:


> Also just on a like for like comparison, if tapwater registers a light orange and aquarium water a very dark "irn bru" orange, and that the source of all aquarium water is from that tap water and I have not added more sulphates, can I not roughly conclude I have more nitrate in the aquarium water?


 I think you probably can, what you don't really know is how much more you've got. If you measured the conductivity of the tap water and the tank water, that should give you some idea of how much saltier the tank water is, and then you can divide that number in 2 to give you a ball park figure for the addition of anions. 





NatureBoy said:


> adding a splash more potassium phosphate has allowed the fissidens to get happy and is creating oxygen bubbles, suggesting there was a phosphate / potassium limit kicking in a day or two after water change.


 Potassium is more likely to be a limiting ion than phosphorus as plants need ~x5 - x10  as much K as P.

If plant growth is better with the dosing regime you are using now, stick with it. If things decline over time, I'd probably go back to EI if you want maximal growth.

cheers Darrel


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## NatureBoy (23 Aug 2013)

dw1305 said:


> Hi all,
> 
> I think you probably can, what you don't really know is how much more you've got.....


 

To that extent the test kit has served a purpose...it knocked my assumption that in my "heavily planted tank" I needed to add as much nitrate as I was, I honestly thought I would get no indication from the test kit, or that I would have a lower reading than the tapwater. So it opened my eyes rather than gave me an accurate reading. For me that's been useful and something that I appreciate the test kit for. Like I say, I've held the test kits in low regard for years, but as a broad indicator it proved a good diagnostic this time.

So I've started to align my parameters closer to the tapwater. The 20ppm Nitrate from tapwater is kind of the target I'm after. Learning that there is 2.5ppm K...but no phosphate provided by the water authority data has given me a starting point for a more "informed" rather than "estimative" index for plant nutrition. I change 25% water every few days and have now started adding a smidgen of potassium phosphate. At the very least it will keep me broadly in line with the tapwater parameters and stop me wandering too far from them.

cheers


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## ceg4048 (23 Aug 2013)

Hello,
		 Unfortunately you are not really any more informed by the municipality report than if you had simply estimated the value at zero and added lots of PO4. I would advise that you stick with an EI dosing program and follow a more structured approach to lowering the nutrient values. The are good reasons for reducing the dosing levels, but being worried about PO4 concentrations is not one of those good reasons.

The behavior of the plants will give you the highest indicator of the nutrient status being sensed by the plants. You never have to worry about adding too much this or that as long as you understand what the effects are to the tank system. High nutrient values enhance growth rates as well as encourage the plants to expel toxic waste products, so reducing the dosages allows you to reduce the water changes, for example. However, nutrient values should be maintained at a high level until the plants themselves indicate that a reduced level is acceptable.

It is never a good policy to trust the test kit or the municipality report at face value when it comes to NPK. For traces this is a different story.

Cheers,


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## NatureBoy (24 Aug 2013)

ceg4048 said:


> Hello,
> Unfortunately you are not really any more informed by the municipality report than if you had simply estimated the value at zero and added lots of PO4. I would advise that you stick with an EI dosing program and follow a more structured approach to lowering the nutrient values. The are good reasons for reducing the dosing levels, but being worried about PO4 concentrations is not one of those good reasons.
> 
> The behavior of the plants will give you the highest indicator of the nutrient status being sensed by the plants. You never have to worry about adding too much this or that as long as you understand what the effects are to the tank system. High nutrient values enhance growth rates as well as encourage the plants to expel toxic waste products, so reducing the dosages allows you to reduce the water changes, for example. However, nutrient values should be maintained at a high level until the plants themselves indicate that a reduced level is acceptable.
> ...


 

Hi thanks for your reply

But why would have I estimated zero? It could have been anything given my prior knowledge, and so this information has again proven useful. The 100microns etc is insignificant at a nutritional level - i want to avoid that level, and now when I add tapwater to my tank I have an informed justification for adding more phosphate, just as others know their magnesium level is low from the tap and add more. I trust that the phosphate level in the tapwater is closer to zero now than say the 5ppm I could have estimated with no real clue. It's about coming from as informed a starting point as possible (such as those who use RO as their starting point) and then adjusting to get levels, followed by water change to realign. This sits well with my rationale for adding nutrients as informed as I can be using tapwater. Fully agree plant / animal / algae appearance is the real guide in all this but I truly believe it's nice to be armed with a cross reference check (the starting point) in order to decide to add more specific nutrients or realign with a water change based on what we see in the tank. 

cheers


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## ceg4048 (25 Aug 2013)

Hello,
The methodology of unlimited dosing means that you ignore the content of the water for the most important nutrients which are N, P & K. Plants need 1000X more N than they need Mg, so it doesn't matter if the water report provides an N value. It's more valuable to assume zero in order to ensure that the nutrient loading is truly unlimited.

The cross reference means nothing because it's entirely possible for the nutrient level in your water to be totally different than what is stated in the report. When the municipality measures water parameters they measure at "representative areas". They may have measurements that are not representative of your particular house and many people assume that the value in the report is the same as the value on in the document. These values are not homogeneous across the measured zones.

The real problem then is that if the municipal report overestimates the nutrient level at your house then it changes your mind set so that you never question the actual nutrient value in the tap water. This can lead to all sorts of problems, wherein the plants suffer nutrient deficiency, but because you are convinced that the nutrient concentration levels are adequate, you will tend to look in the wrong places for solutions.

You can never actually be informed about the nutrient levels in the water. Having said that though, if you live in an agricultural zone, then there is a high probability that the water is high in nutrition due to runoff.

Apart from all that, even if the water report is accurate, there is really no value in that accuracy. Being accurate does not help you to grow better plants in a CO2 enriched tank. That's a certainty.

Cheers,


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