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Dry ferts - please help me with the maths

daizeUK

daizeUK

Member
Joined
18 Jun 2013
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161
Location
Berkshire
I want to dose my 120L tank with Potassium Phosphate and Potassium Sulphate
I'm trying to figure out how many grams of each salt to add to a 500ml solution. I want to work in grams rather than teaspoons so that I can work out how much salt to buy and how long it will last.

APF tells me to mix Potassium Sulphate like this:
Stock solution : Add 6.5g of potassium sulphate to 500ml of water. Dose 1ml per 10 litres Of Aquarium water 3 x week; this will add approximately 1.5ppm K

SoI took this to the nutrient calculator at Yet Another Nutrient Calculator which tells me the EI target for potassium sulphate is 7.5ppm. So I work out that to dose my 120L tank for EI levels I should add 60ml of the stock solution suggested above (120L/10L x 7.5ppm/1.5ppm).

The problem is that when I ask the calculator to work out how to make a solution based on that dosing and it didn't agree with APF.
These are the values I plugged in:
My aquarium is 120L
using diy fertilizers
I am dosing with K2SO4
using a solution
My solution container is 500 mL and each dose is 60 mL
and I am calculating for The Estimative Index

I expected it to tell me to make the solution with 6.5g of potassium sulphate but it doesn't:
To reach your target of 7.5 ppm K you will need to add 16.714 g K2SO4 to your 500.0 mL dosing container. Add 60.0 mL of that mix to your 120.0 L aquarium

Why are APF and the calculator telling me different amounts? Is one of them wrong or have I made a mistake somewhere? :confused:
 
I completely agree with John. You are wasting your time and energy trying to calculate dosages to the nearest 1/1000th of a gram.

1 teaspoon of powders typically weighs about 6 grams, so just do the conversion and get on with it.

Also, if you are dosing Potassium Nitrate then you absolutely do not need to add Potassium Sulfate. So that's one less thing to calculate.

Cheers,
 
I've got no intention of measuring doses to the milligram and I totally understand that it doesn't have to be accurate but I get the feeling that the APF site is giving incorrect concentration advice there. If I followed their instructions I would only be dosing 40% of the potassium I need (assuming the calculator is correct).

The phosphate calculations also seem to be inconsistent. If I follow your guide and convert it into grams for my 30 gallon tank it works out as about 500mg KH2PO4. The TNC calculator roughly agrees with this at 660mg KH2PO4. The Petalphile calculator gives me 211mg KH2PO4. I don't mind being inaccurate to say, 50% but this is just silly. One of these calculators will either have me triple dosing at 300% or underdosing at 30%.

Tom advised me to use potassium sulphate since I already have 40ppm nitrate in the tap water (and enough magnesium, but no potassium or phosphate). However you also told me this:
ceg4048 said:
The dynamics of nutrient uptake and usage are generally optimized around regular and cyclic dosing.
Click to expand...
Can you explain the biochemistry of why regular nitrate dosing would provide better benefit than adding 20ppm of nitrates via a weekly 50% water change?
 
daizeUK said:
One of these calculators will either have me triple dosing at 300% or underdosing at 30%.
Click to expand...
But this is not a problem. There will still be plenty of nutrition, and that's why you shouldn't worry about it. Have a read of the thread EI Newbie, totally confused lol | UK Aquatic Plant Society

At the end of the day, we can always tailor the nutrient dosing to fit our objectives. You are not locked into any formula. You just have to avoid deficiency. The baseline dosing levels are so high that unless there is a flaw in flow/distribution you shouldn't see a problem no matter which recipe is used.

daizeUK said:
Tom advised me to use potassium sulphate since I already have 40ppm nitrate in the tap water (and enough magnesium, but no potassium or phosphate).
Click to expand...
Yes, of course, that's true if it is confirmed that the NO3 levels are actually that high. But I never assume that is the case unless the plants themselves prove that I do not need to add Nitrogen. Nitrogen is at the very top of the food chain so I never make assumptions about it's availability. I always start first with the baseline and then withdraw the KNO3 to see if it makes a difference.


daizeUK said:
Can you explain the biochemistry of why regular nitrate dosing would provide better benefit than adding 20ppm of nitrates via a weekly 50% water change?
Click to expand...
Well, one of the reasons is that plants have two basic categories of nutrient uptake. A low affinity system, which does not grab the nutrient molecules as eagerly, and a high affinity system, which aggressively attracts the nutrient molecules.

The low affinity system is enabled when the nutrient levels are high. This means that nutrient availability is high and the plant does not need to spend energy producing those high affinity proteins. They are expensive to produce. The resources can then be spent on other things.

When the nutrient availability is low, then the plant is forced to produce these aggressive proteins in order to ensure sufficient nutrient uptake.

So what happens is that when you dose high amounts infrequently, the nutrient availability skyrockets initially, growth increases quickly and the plant drops production of the high affinity system components. The plant calibrates it's systems to the high nutrient load. Then, later in the week, when the nutrient values decline, the calibration becomes invalidated. There plant now has more mass and expects to have the high nutrient load, but it is no longer present. Nutrient uptake rates decline and the plant then tries to engage the high affinity system.

All of these changes takes time. They don't happen overnight. So the plant is trapped in a continuous loop of switching from low affinity to high affinity while uptake rates suffer at some point in the loop. Over time this reduces their efficiency, and generally their health will suffer. Again, this does not mean that it will always happen, or that it always will be terrible. This is just a general pattern.

Cheers,
 
Thanks for that great explanation Clive!

I'm afraid my curiosity wouldn't let me leave the maths alone! :) Perhaps it may not matter, but I didn't like not knowing which calculator to believe so I sat down and figured it out myself.

The EI target for phosphate is 3ppm, or 1ppm thrice weekly.
My tank is 120L therefore I need 1ppm x 120 = 120mg of Phospate thrice weekly, since 1ppm is equivalent to 1mg/L when dissolved in water.
The molecular weight ratio of phosphate to KH2PO4 is 94.97 to 136.09 = 0.7.
Thus to get 1ppm of phosphate I need to add 120mg / 0.7 = 172mg of potassium phosphate.

If I've made any glaring errors then do point them out! Otherwise my value is even lower than any of the online guides and calculators suggest. I'd be interested to know why some of the suggested values were so much higher.
 
Hi daizeUK.

As mentioned, it's not so important you get things exactly right, but I can certainly understand your frustration when tools do not work correctly.

I think you may be doing the calculation on my calc wrong. Here are your numbers above, which match mine perfectly. Are you sure you didn't pick K2HPO4 or something else?

bbnobdn.png


Cool imgur upload thingy by the way, UKAPS!
 
Cheers wet,
That calculator uses 1.3ppm as the PO4 target for EI (if you ask it to calculate for Estimative Index), otherwise it does agree with my calculations exactly. I used a target of 1ppm because Clive's thread says the EI target should be 3ppm per week. I'm curious why other calculators seem to have completely different targets, e.g. the TNC Calculator advises a dose of 660mg KH2PO4 which would give 3.84ppm or 11.5ppm per week which seems excessively high! Clive's recommendation of 1/16 tsp per 20 gallons would give about 3ppm per dose.

So I'm wondering if there is a reason for these high doses, I suspect the latter is an arbitrary amount because 1/16 tsp was the smallest convenient measurement for that example, but I'm curious to know why the TNC calculator is recommending nearly 4x the EI target.
 
I can't speak for the TNC calculator, but the PO4 targets for EI come from a Plantbrain post on his forum a few years ago. I just chopped it up a little and posted it back and everyone seemed pretty cool with it once we talked it out :) Remember you can always pick one of the other presets, though, like EI Low Light or EI Daily (but only dose like every other day or something).

Here's the values for dosing in case you want to scroll through them. I find it interesting and kind of shows how close they all are. (Check out ADA and what AquaSoil adds vs EI for example.)

Links are breaking but here it is:
yet-another-nutrient-calculator/constants/dosingmethods.yml at master · flores/yet-another-nutrient-calculator · GitHub
 
Whoops, I guess I never added the ADA stuff to the calc. If you guys want it I can get around to it.

Here it is with some explanation. Reverse engineered from Plantbrain's measurements vs recommended dosing on the bottle. It's totally weird though and I don't get how some of the bits work with ADA and combining bottles :)

Links on the forum are trying to get too much data but it's below here:
using Plantbrains concentrations and rota.la to get ppm/mL, then manufacturer dosing.

*NO3 is derived from total N as NO3 equivalent. There is some NH3/4 in ADA fertilizers. Use rota.la to get NH3/4 specifically
 
As I mentioned in that thread I linked to, it would be better to forget about any differences in the various recopies. EI is not a recipe. It is a world view. It is a methodology and a perspective which owes no allegiance to any formula or any recipe. It is an exercise in irrelevancy because you can dose any value you want and it will have the same effect. You should not care or spend energy worrying about why Recipe X is higher than Recipe Z. There are plenty of things to worry about in a eutrophic, CO2 enriched tank. You should be worrying about how you will accomplish excellent CO2 distribution, NOT why Tesco cat litter cost so much less than the same brand found at Sainsbury's.

I do not limit myself to any recipe. When there are good reasons to use lower values, they can be used without any concern. If you want to use higher values then you can without any reservations whatsoever. You don't have to worry about toxicity or algae because nutrients don't cause algae. Dose whatever values necessary to ensure unlimited nutrient availability. THAT is EI. I do not care about the recipe. I've actually only used those numbers you see in the article a handful of times. I'm a an obsessive water column doser so I dump lots of powder into the tank just to see what happens.

Here is a tank obsessively dosed with 10ppm PO4 per week. Who cares?

8394115845_d7ca6ffd66_c.jpg



Cheers,
 
Isn't pushing your "world view" completely ignoring that some folks may look at their tanks differently than you do, and does your view consider that dismissing that or tools to help them may actually discourage them?

"I do not limit myself to any recipe."

Yes you do, dude. Read your post again and how you dismiss others.
 
I am sold on the idea that unlimited nutrients offer the best growing conditions for plants and therefore EI provides the best method for a planted aquarium.

I'm not yet subscribed to the notion that chemicals can be added arbitrarily without regard to toxicity, unless you can point me to scientific evidence that shows that high nitrate or phosphate levels have NO effect on the health of ANY species I might care to keep in an aquarium - including sensitive shrimp species which are noted for their intolerance to nitrate, for example. When I say no effect I also want to consider general comfort and long-term effects on longevity and organ function, not just that the animal doesn't drop dead tomorrow.

I'm also tight-fisted by nature and I prefer not to waste chemicals fecklessly if there is no further benefit to the plants :)

If I understand correctly, Tom Barr proved that there is a cap to all nutrient and light levels beyond which a plant cannot grow any faster. So, EI does have a recipe which is derived from these capped levels. Assuming that CO2 distribution is perfect, what is the benefit to anything by exceeding these limits?

Thanks for your links, wet! I hadn't realised the calculator was yours! ;)
 
I really like where you're going with this.

Personally I am not down with dumping say 40ppm of NO3 (or moving CO2 quickly, or anything big and fast in an aquarium) into a tank with living things. I have the same mindset you do that even if I cannot observe behavioral issues, my thinking I *may* be raising toxicity in a tank doesn't jive. Like, it's not worth me even worrying bout it, especially when considering the max yield vs concentrations you cite from Tom.

One more data point: Claus (the former Tropica guru, still guru) likes to under fertilize his tanks because he wants to limit growth. That can make for a nice easy tank :)

I would suggest you start low, as you're intuitively doing, and then slowly ramp up. If you already have some established plants, watching them as you adjust dosing over weeks will tell you tons about the tank. Then post back about those plants and try more and harder plants. Or at least that's how I recommend it to new folks. It's fun that way :)
 
daizeUK said:
I am sold on the idea that unlimited nutrients offer the best growing conditions for plants and therefore EI provides the best method for a planted aquarium.

I'm not yet subscribed to the notion that chemicals can be added arbitrarily without regard to toxicity, unless you can point me to scientific evidence that shows that high nitrate or phosphate levels have NO effect on the health of ANY species I might care to keep in an aquarium - including sensitive shrimp species which are noted for their intolerance to nitrate, for example. When I say no effect I also want to consider general comfort and long-term effects on longevity and organ function, not just that the animal doesn't drop dead tomorrow.
Click to expand...


You're asking for something that is impossible to deliver, unless you have a few tens of millions lying around in cash and want to commission the research yourself (if so give me a shout, I'm at a loose end).

If you're that concerned about fish health in relation to chemical addition, why are you running a high tech tank at all? EI is an arbitrary amount, simply designed to be nutrient unlimiting for any realistic tank setup. Why do you think that 'base' EI levels have no long term consequences for fish? Are you adding CO2? How are you determining a safe CO2 level?

Sorry to be a bit blunt, but building a straw man on fish health grounds is pretty weak, particularly in a high tech setup with all the associated possibilities for behavioural and physiological stressors. Do you have evidence that how you keep fish now has no impact on their comfort, longevity and organ function, compared to in the wild or in a completely optimal environment? How are you defining and measuring comfort?
 
I have seen a fair amount of scientific research on the effects of ammonia on fish physiology. Sadly it is mostly aimed at commercial fish farms but some of it is relevant to aquarium fish and I have been particularly interested in research on the long-term health effects upon fish from sustained sub-lethal levels of ammonia. The research can be hard to find, particulary research that is free to the public, but there is still plenty of information available in this area.

When I look into this sort of research I am defining and measuring comfort via physically measurable effects such as length of lifespan, gill hyperplasia, evidence of kidney damage etc. These are all useful indicators on how much physical distress a fish is experiencing. In the case of ammonia I am also looking at whether these effects are reversed once the fish is re-introduced to clean water or whether the damage is permanent. Experimental studies exist that have measured all these things via biopsy and autopsy.

Thus I was hoping that something similar existed for studies upon phosphates and nitrates and that you guys might be able to point me to it. Perhaps the most likely source would be studies upon the effects of freshwater river system pollution from agricultural fertiliser run-off.

My point is that the claim is being made here that it does not matter how many nutrients are added because it has no effect on the tank inhabitants. I'm simply asking to see the evidence that this claim is based on. If you think there is no evidence then how can the claim be valid?
 
"Test it and see. I'm not going to answer this because you or someone else should do this, then they will know the TDS contribution from dosing." - Plantbrain

Exactly. Don't assume it. I feel like people are only reading half or less of Plantbrain's lessons.

I would not say there is anything matching daizeUK's request for definitive data in that thread. Yes there is Plantbrain's experience, which is valuable. But that is not definitive data.
 
daizeUK said:
My point is that the claim is being made here that it does not matter how many nutrients are added because it has no effect on the tank inhabitants. I'm simply asking to see the evidence that this claim is based on. If you think there is no evidence then how can the claim be valid?
Click to expand...

To my understanding Its apparently really hard to get accurate data on specific parameters in the aquarium without being rich as Tom mentions. So for us as people who are doing this as a hobby its really hard if not impossible to give accurate data. Although looking at fert pollution in rivers may give some sort of comparison we must note that the main request is about the health of fish in a enclosed system so we can only use data from that to an extent. So really in order to answer you question it may be easier for you to experiment yourself like wet's quite from T.B. Even then you may have to look at ethical issues.Therefore asking for definitive data is quite a hard task.

I'm sure members on this forum have experienced dosing large amounts of EI with fish in their tank without causing problems, maybe asking about their dosing levels and observations in their fish's health to see if there are any correlations rather than asking for highly technical evidence such as autopsies or similar.
 
Thanks Michael. I'm happy to look for research myself if nobody has any links. I'm afraid I'm not qualified to experiment myself, as I have no training in biology or veterinary science :)

Just to be clear, I'm not questioning whether base EI dosing is safe. Plenty of people use it and are happy with it and that's fine with me. My concern is about the unqualified advocation of arbitrarily high dosing levels, especially without knowing if there are potentially sensitive species present.

For example when I see a blanket statement such as
ceg4048 said:
Overdosing of npk or trace will not affect fish.
Click to expand...
I'd like to know what this statement is based on and whether it has been tested on all species at all levels of dosing. If not, then shouldn't it at least be qualified? Where are the safe limits? Which species are the exceptions, if any?
 
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