Chempak & Dosing Calculator

drjack

Member
Joined
10 Jul 2011
Messages
36
Location
Colchester
Hi, I have two question both involving calculations, I must add I am not a chemist, but I really could use the help. I my tank is low tech/low light and I have very hard water living in Colchester.

Question 1 - relates to a post in January this year on Help with all-in-one recipe, on how much Chempak sequestered iron to add to a tank. The link is:
https://www.ukaps.org/forum/threads/help-with-all-in-one-recipe.59689/

Extract from the post said:

@dw1305 i followed the link you sent:

"So our fertiliser has 20,000 ppm of Fe. If we take 1g of "Chempak sequestered iron" and add it to 1 litre of water, we've divided 20,000/100, so we have 20 ppm Fe.

We want 0.5 ppm, which is equivalent to 1g in 40 litres (20/0.5 = 40).

You have a 450 litre tank, so we can multiply by 10 to give us how we would need in 400 litres of water: 1g x 10 = 10g and then add add on the amount we would need for the extra 50 litres, = 1.25g (40 x 1.25)

Total amount of "Chempak sequestered iron" to give ~0.5 ppm = 11.25g in 450 litres."

Given mine is 280 and I'm using the same fertz - I need a total of 7g (280l / 40 litres=7g) to give me 0.5 ppm. How do I work that out for my 1 litre all in one mix which adds 50 ml as an overall dose?

Chempak total iron is 2%. I understand everything in the posts before the line in RED and after it. What I can't get my head around is why is 20,000 divided by 100 and if that's correct why is 20,000/100 = 20 and not 200 ??? I just want to understand what I am doing before I dose the Chempak.

Question 2 - relates to the UKAPS nutrient calculator. I am about to restart using my APF dry salts. The APF recommended mix in 500ml water is 4 tsp KNO3 + 1 tsp KH2PO4 which I have used in the past. But when I use the calculator it recommends in 500ml water 3TBLS + 1 tsp+1/2tsp+1/4tsp+1/32tsp KNO3 and 1tsp+1/8tsp+1/64tsp of KH2PO4. While the amount of KH2PO4 is very similar the amount of KNO3 is higher by about a factor of 3. Is there a simple explanation for this?

I guess I should have paid more attention in chemistry class 50+ years ago.
All help really appreciated

Kind Regards, David
 

dw1305

Expert
Joined
7 Apr 2008
Messages
10,938
Location
nr Bath
Hi all,
Chempak total iron is 2%. I understand everything in the posts before the line in RED and after it. What I can't get my head around is why is 20,000 divided by 100 and if that's correct why is 20,000/100 = 20 and not 200 ??? I just want to understand what I am doing before I dose the Chempak.
It is probably me lost in the <"powers of 10">.

cheers Darrel
 
Last edited:

drjack

Member
Joined
10 Jul 2011
Messages
36
Location
Colchester
Hi Darrel,

Thank you for that, I thought I was having a senior moment:). Could you help me with what follows the RED line. If my tank is 180 litres then the above would read if it should be 200ppm.

We want 0.5 ppm, which is equivalent to 1g in 400 litres (200/0.5 = 400).

I have a 180 litre tank, so we can multiply by 180/400 to give us : 1g x 180/400 = 0.45g (or ~1/16tsp)

Total amount of "Chempak sequestered iron" to give ~0.5 ppm = 0.45g in 180 litres."

Does that look right or have I made a mistake? Also, why do you divide by 100 in the RED line?

Any thoughts on my second question regarding KNO3?

Kind Regards, David
 

Zeus.

Member
Joined
1 Oct 2016
Messages
3,362
Location
Yorkshire,UK
relates to the UKAPS nutrient calculator. I am about to restart using my APF dry salts. The APF recommended mix in 500ml water is 4 tsp KNO3 + 1 tsp KH2PO4 which I have used in the past. But when I use the calculator it recommends in 500ml water 3TBLS + 1 tsp+1/2tsp+1/4tsp+1/32tsp KNO3 and 1tsp+1/8tsp+1/64tsp of KH2PO4. While the amount of KH2PO4 is very similar the amount of KNO3 is higher by about a factor of 3. Is there a simple explanation for this?

APFUK is EI Dosing as in the EI range

1600949064565.png


But how much of each varies from user to user eg my WC delivers 10ppm NO3. Its just a case of making sure your plants have enough
 

drjack

Member
Joined
10 Jul 2011
Messages
36
Location
Colchester
Hi Zeus, thanks for the reply. If it is just a matter of being at the higher end of a recommended range that's fine. I was just curious as to why for KNO3 it was so different.
Many Thanks, David
 

drjack

Member
Joined
10 Jul 2011
Messages
36
Location
Colchester
Thanks Darrel, much appreciated looks like I need 4.5g for my 180L tank. Just for my own education, as above, "if our fertiliser has 20,000 ppm of Fe. If we take 1g of "Chempak sequestered iron" and add it to 1 litre of water, we've divided 20,000/1000, so we have 20 ppm Fe" ..... why do we divide 20,000 by 1000 to get a different ppm? Chemistry was never my strong point.

Thank you for all your help, David
 

dw1305

Expert
Joined
7 Apr 2008
Messages
10,938
Location
nr Bath
Hi all,
"if our fertiliser has 20,000 ppm of Fe. If we take 1g of "Chempak sequestered iron" and add it to 1 litre of water, we've divided 20,000/1000, so we have 20 ppm Fe" ..... why do we divide 20,000 by 1000 to get a different ppm?
It is back to the percentage of iron (Fe) in the compound and the "powers of 10" when converting from grams per litre to ppm (mg/L).

There are 1000g of water in 1 litre.

Our compound is 2% Fe which means that 1 g of chelate contains 0.02 g of Fe. After that there are 1000 mg in 1 gram (10^-3) so 0.02g is 20 milligrams and there are 1000 micrograms in a milligram (10^-3), so that 1 microgram per gram is equivalent to ppm (10^-3 + 10^-3 = 10^-6).

We have 20,000 micrograms in 1 litre and 1 litre is 1000 grams, so to get to ppm (mg/L) we divide 20000/1000 to give us 20 ppm (mg/L).

That is why you tend to get errors by one order of magnitude, it is really easy to get lost in the powers of 10. I've been using scientific notation (and mg/L rather than ppm) with our students, because it makes the relationship a bit more obvious and removes one stage in the calculation.

When I do this quickly for a UKAPS question I just use mental maths. and guestimation so I already know whether the end weight is likely to be nearer to ~10g or ~100g. If I need to do it properly I use a spread sheet with a periodic table and some built in error checking.

cheers Darrel
 
Last edited:

drjack

Member
Joined
10 Jul 2011
Messages
36
Location
Colchester
Thanks Darrel for taking the time to explain. Who thought keeping fish would this complicated.:)
All the best, David
 

dw1305

Expert
Joined
7 Apr 2008
Messages
10,938
Location
nr Bath
Hi all,
Who thought keeping fish would this complicated
I know.

It is a bit of a <"strange analogy">, but I always think it is like a cappuccino. I'm interested in the coffee, I'm not interested the froth, but the problem is how can you tell <"where the coffee ends and the froth starts?">.

That is why I need to write a more coherent version of page 4. <"Bedside Aquarium">. I want to quantify as much as possible what are the really important bits? What is <"always the Coffee?">

The idea behind the <"Duckweed Index"> was that you just drank and enjoyed the drink, you didn't need to worry too much about the minutiae.

cheers Darrel
 

Similar threads

Top