Always Broke said:

Looked at that and I must say I understood absolutely nothing it tells me .

I need some explanation.

Oooh, oooh, I love this graph. It's an anoraks dream. I've been trying to explain this to the nitrate haters for ages. Type in the following numbers at the top:

In the "I am adding" field (type in 8 ppm)

In the "times a week" drop down box (select 3 times a week)

In the "I'll Change" field (type 50% water)

In the "water every" drop down box (select week)

Then, click the "Graph me!" button.

The number that you typed/selected could be a typical EI KNO3 dosing scheme with a weekly 50% water change. That's got to be obvious right?

Many people fret about nitrate buildup because they are coming from a fish only environment, and they've been programed their whole lives by The Matrix that the reason for a water change is to get rid of built up nitrates. Little do they realize that nitrates are only the smoking gun and that the real culprit is the organic waste that the nitrates started out as, i.e. ammonia.

Just like in The Matrix people hang on for dear life to these concepts and this graph shows what the maximum build up level of nitrates, or any ingredient would be if you dose. Of course this graph can't tell you about the build up level from organic sources in the tank, which would have to be added to these numbers. It's just a mathematical execise to show you what would happen if you dosed a certain amount every week and if you then did a certain amount of water changes. As long as you stick to that schedule of adding and changing, this will be the build up result.

Using our numbers we can see that the worst case scenario if the plants

__did not__ use any NO3 at all. That's the red graph.

The horizontal axis is the passage of time in days. You can see the markers are in groups of a week - 7 days, 14 days and so forth.

The vertical axis is the concentration buildup of whatever we are adding, so lets just say we are adding KNO3. If this is the case then the graph shows you the maximum build up of NO3 in the water column over then following weeks. The Red graph assumes that the plants are not using any NO3. So the worst case scenario for our selected dosing and water change schedule with zero nitrate usage by the plants means that the NO3 cannot exceed 50ppm. This is an important graph for the nitrate haters because it shows that after about the 4th week the NO3 levels due to dosing cannot exceed 50ppm, even if you continued this dosing strategy till the end of days.

Of course, the plants absolutely will use NO3. That's what they do. The more light and CO2 pumped into the system, the more they will consume. The consumption is referred to as "uptake". The successive colored graphs show the maximum buildup assuming successively stronger lighting and/or successively stronger CO2.

So if the plants are consuming 25% of what you dose then the pink graph applies and therefore the maximum buildup of NO3 that can occur with the scheme we entered will be around 35ppm. At 50% uptake by plants then the blue graph applies and the maximum possible build up the tank will ever see is about 25ppm.

Why is the graph a jagged sawtooth shape? Well remember what we're doing. 3 time a week we are adding 8 ppm so we start off with 8ppm, then there is a second plateau when we add the second dose, and of course there is a third plateau when we add the third and final dose. On or around the seventh day there is a water change so some NO3 is removed and the concentration level drops. Then we start adding the NO3 again, so the concentration level starts to rise.

Again, the calculator cannot tell you how much organically derived NO3 will be there, nor can it take into account NO3 that may be in the water you are using for the water change, but it does show you the maximum effect of build up due to your dosing scheme. If you alter the added ppm or the percent of water change or the frequency you can re-graph to show the changes in the maximum build up.

So this would be very useful, say, if you knew you couldn't manage a weekly water change, only bi-weekly. The maximum achievable build up would then rise, so you could enter a different dosing number to bring the max build up value down. Play with the numbers. Change to "every two weeks". You see the maximum build up change to near 80ppm for the red graph. If this worried you then go back and lower the added ppm to 4. Then you see the max buildup drop back down to near 45ppm.

LondonDragon said:

I still struggle to comprehend what is right in terms of ppm, I just use the recommended values for EI and then add a little extra.

Paulo, you struggle because you refuse to let go of the the concept of "right". There is no "right", but there may be a "wrong". Wrong is made plain to us by failed plant health, which often results in a deficiency syndrome. Stop thinking in terms of "Right". The ppm values are just a guide. They can show you the path. Also remember that these number have to be considered within the context of flow/distribution, lighting and CO2.

Cheers,