Bob, this is why we need to understand the fundamental arithmetic of our dosing program. You really ought to study the EI Tutorial. Ask questions if the statements seem unclear. That way you'll have a firmer grasp and will find it easier to interpret any anomalies that arise.
The FluidSensor page quite clearly states that the values being provided are a one week supply:
500 ml will provide up to 4 doses for your size tank
(That is up to 1 weeks supply of Macro solution and
up to 2 weeks supply of TNC Trace solution)
If this is the case, then only 4 doses worth of macros are being mixed with the water and therefore the total volume of the mix is divided by 4. It doesn't matter what the volume of water is. You can put 4 doses of powder in 4 gallons of water. Each dose will then be 1 gallon but will contain exactly the same number of grams of powder as if you mixed the powder in only 500ml of water.
In the EI Tutorial I elected to make up a batch that would last 12 doses, i.e. 1 month supply:
1 month = 4 Weeks
3 doses of NPK per week
Therefore there are 12 doses of NPK per month.
...
Now this mixture must serve 12 doses so each dose is 600ml/12 = 50ml
This makes life easier because you need only dose 50ml of this NPK solution 3 times per week.
If you understand the fundamentals, then you realize immediately that it's no big deal to multiply the FluidSensor values by 3 in order to get the 12 dose equivalent amount of powder. You can even simply multiply the single dose value of KNO3 (3.7g) by 12 to arrive at about 45g.
Then you can divide the volume of water by 12, i.e. 500/12 which gives you roughly 40ml doses.
it's really important that this makes sense, even if you have to struggle to have it resolved in your brain internally, otherwise we'll forever be tripping over our own shoelaces.
It's not clear to me why they chose a 1 week supply as opposed to a 1 month supply, but that's something you should ask the guys on the FluidSensor forum thread =>
Bryan's (not very) Secret Project.....UPDATE which they opened a few weeks ago. Due to forum guidelines they can not comment on this thread.
Cheers,