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Problems with Phosphate level under EI regime


19 Oct 2008

Hi, Have been using Estimative Index, since November. This is currently working on a routine of 2 water changes of 20% a week.

The formula for my dosing liquids are included below from my original posting back in Oct / Nov

Using James' planted tank calculator, I carried out the following maths:
1000ml solutions, dosing 25 ml per dose of macro and trace solutions. (Keep both the same, keep it easy!)

All the figures below have been slightly rounded where sensible.

Macro solution (1000ml):

Potassium Nitrate 162 g (27 teaspoons) = 3 x 10ppm doses per week
Potassium Phosphate 29 g (4.5 teaspoons) = 3 x 2ppm doses per week

The above two amounts also provide 3 x 7ppm doses of Potassium per week.

Trace Solution (1000ml):

60g provides correct amounts for 2 x 25ml doses per week.

I was getting a lot of hair algae but no other type. I have now got about 30 largish Amano shrimp in the tank and they keep it absolutely spotless. They are the most amazing ally in the tank!

However, I thought I ought to do a water quality test just to keep an eye on how things are.

Everything looked good, no high level of Nitrate or Nitrite, No ammonia, things looking hunky dory until I got to Phosphate. Never had a problem with this, and the water going into the tank has a phosphate level of almost 0, so I was shocked to see the phosphate level in my tank is over 5 mg/l.

Surely this isn't healthy, or good for the dicsus in there? How come the plants seem to be using everything they're provided with except the phosphate? Does this mean I got the amount of pottasium phosphate in my macro mix hideously wrong?

Should I try and get the phosphate level down, or just mix up a new macro mix with less pottasioum phosphate and keep going with the dosing regime?

Any thoughts appreciated.



19 Jul 2007
Lincoln UK
How are you testing? almost 0 from tapwater sems a bit low to me in the UK.

You will also have some P from the heavy feeding of discus!!!



Expert/Global Moderator
11 Jul 2007
Chicago, USA
Yeah but the real question is: Why are you testing and why is someone who is dosing EI suddenly a phosphate hater? In the first place, there is enough evidence to show that hobby grade test kits are unbelievable, so no matter what readings you get they are to be ignored anyway because they are more likely to be completely wrong in either direction. If you are dosing EI then you know exactly how much N, P and K are being dosed into the tank so why would you need to test them? Secondly, it's much better to have high numbers than low numbers.

So for example hair algae is associated with low CO2 so you need to add more CO2 not less. The fact that you are not suffering GSA or BGA means that your PO4 levels are fine and that your nitrate levels are fine respectively. Testing and then panicking about test results is what really causes algae.

Are your discus suffering? Are the shrimp suffering? By all accounts they have strong appetites so what's the problem? How soon would the discuss start to suffer if you didn't do any water changes? Fairly quickly right? Yet you are adding all this PO4 and they haven't skipped a beat so how could anyone draw the conclusion that somehow high PO4 is "hideous"?

In my opinion your best bet is to throw away those hideous test kits and to Carry On...



2 Aug 2007
Hair algae means one thing, you do not have decent CO2, you are adding some, but not quite enough.
You have ruled out all the other nutrients if you dosed EI....................but have not addressed CO2, light seems fine so we can check that off.

We can add 5ppm of PO4 also, without even inducing algae(I can do it right now and without a lick of fear because I knwo what will occur).

What's the difference? I'm pretty sure things are fine because my CO2 is well tweaked.

CO2 is the issue, it's 95% of all issues folks have and it's easy to rule out light and nutrients issues.

So then you are left with good stable CO2.

Note: you can add Easy Carb or Excel and also do a blackout for 3 days, you can do a larger water change and add excel directly on non living rocks etc to kill anything on them, you can add algae eaters, like SAE's etc.

But the bottom luine and root issue is still CO2.
Make sure you progressively and SLOWly add more and make sure there's some surface movement etc, watch fish carefully.

Do not get in a rush and add too much and then leave for the day.

This is key and a good lesson for you to focus on and learn to address, CO2 is most of this issue with algae and with excellent plant growth. You learn this, then the rest is much more about gardenign and plants, not algae.

Note: adding PO4 can cause a dramatic increase in the uptake of CO2 by plants, so if you had been adding just barely enough CO23, but had limiting PO4, adding PO4 would appear to cause algae, however, it's an indirect effect, the root issue was CO2 was not scaled up and that, not the PO4 itself caused the algae.

This is why I can have no algae with 5 pppm of PO4, whereas you might dose PO4 and get algae each time, leading to not believe me and simply do what you can to minimize algae. I understand the thinking and results from that experience, many saw this.

Unlike them, I saw and looked at other possible causes, I looked for the root issues. when I aded more light, I knoew that this causes more CO2, anyone that adds medium to high light knows they need to add CO2. common sense and advice there right? It made sense to add more CO2, so back 15 years ago, folks added 10-15 ppm of CO2, but only had 1/2 the light my MH 's added, so I doubled the CO2, fish where fine(have been ever sense).

Now when I added PO4, no algae.
If you scaled the light up, and the CO2, then add the nutrients to also non limiting levels, you have no issues.

If not and you limit say PO4 strongly then the plant will limit the uptake of CO2 and NO3 etc, K+ and so on, since the plant does not need those and is most strongly limited by PO4, thus PO4 controls all the metabolism, not CO2.

When the PO4 limitation is lifted, now you have placed more demand on the CO2, NO3, traces, K+ etc.

So focus there on CO2, it's worth your while and you will gain a lot from doing so.
You might have to eyeball things well.
Also, Discus will turn dark at over 45ppm of CO2(large wild adults etc). So you can watch them to some degree.

Hope this helps, forgive these folks on the PO4, they have heard this claim that it causes algae for a long time and know better, so they get a little wryly :D
It's okay, I understand! Been there.

Tom Barr

Tom Barr

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