Nutrient burn?

[urbanfarmer]

Oh, you actually meant using some kind of resin. No, I do not recommend this in aquaponics. Less is more! Use less chemicals to get more vigorous and healthy plant growth!

pH buffering is not caused by something that acts on the acid you are adding, but it is the acid itself... citric acid will act as a buffer to lowering the pH whereas sulfuric acid will not... again, it has to do with the pKa value and the species caused by the interactions therein...

There must be something else going on for the pH to bounce from 3.5 to 8.0 because that is an ion differential of around 50,000x TIMES which is an enormous amount... enormous... amount... there really are too many things to consider as to why you would observe this, most of which fall under the category of human error, but without specifics there's no way to tell.

The reason plants can take up nutrients when concentrations are low with more moving water is not because nutrient uptake is cumulative... it's a bit more complicated than that

[rfeiller]

The resins are in tanks ion exchange resins are used throughout the water Purification industries. In fact much of the time it is part of the bottled watet process. And I disagree about your statement on buffering capabilities of alkalis and acids.

[urbanfarmer]

The resins are in tanks ion exchange resins are used throughout the water Purification industries. In fact much of the time it is part of the bottled watet process. And I disagree about your statement on buffering capabilities of alkalis and acids.

But sir, I don't want to DRINK my AP water...

Aren't you using RO water? How would you get acids/bases with their conjugates in the water... You have ammonia in the water, but at a very low molar density... Also, you are discussing strong and weak acids, but you don't seem to draw a distinction between the two. You realize they act differently in solutions with or without a buffering solution present, yes?

Here are some good videos on buffer calculations:

Part 1: http://www.youtube.com/watch?v=hWkXoHqHyfs
Part 2: http://www.youtube.com/watch?v=rLPc8Rcxnmk
Part 3: http://www.youtube.com/watch?v=2fvD_kf_KIE

There are many things to consider in the interactions, and without specifics we can't really say for certain. However, it's not magic; there is sound science from which to base our decisions... pH interactions are probably one of the simplest (yet the most important) aspects of our AP systems...

[rfeiller]

as long as the tap water is sierra tap water (melted snow) it comes through at about 7.0pH less than hundred ppm of total disolved solids. i do not us RO at that point. it is when the batch plant mixes in well water that can be over 8pH and tds of 400 or better that i use RO. but all of the water runs through a GAC tank prior to being added to greenhouse plants, koi pond or fish tanks.
the purpose of DI resins is to exhchange out unwanted elements of the water. i do not add chemicals to the water and prefer not to use any buffering solutions such as pH up or pH down that just adds one more thing for the fish and plants to deal with. some prefer to use DI resins over RO it is more convienent when recharged than dealing with a RO holding tank. to me it requires more work because it has a ppm limitation between recharging. it is not uncommon to mix several different methods of dionization to achieve the desired results including multistage distilation or a slow natural form of ion exchange by using acid peat, most of the peat available in stores lacks the low pH of 3.5-4 and can be partially neutralized.