Here is what canna had to say
Re: CANNA Form Submission
The first thing I'd recommend is ditch the air pump, it has no place in the reservoir, especially that you have a very powerful one.
What the air pump does is push and diffuse into solution a ton of airborne microbes, bacteria, fungi etc... all of which are likely to be the source of the slimy build up you are seeing.
Secondly, above 22c you are favoring the development of such microbes. [clean that tank and equipment very well with a 1:10 bleach solution when you get a chance]
We do need to have circulation in the tank (ideally taking water at the bottom and releasing it at the top), to prevent stagnation, a 640 gph pump in a small 25gal tank is more than enough to to so.
that pump is likely to be generating that extra heat we don't want, perhaps have it on a timer? or cyclestat like 1 minute on 15 minutes off... or whatever
nutrient solution does not need to be continuously stirred either.
Another side of air pumps that is detrimental and likely to cause what you are seeing in terms of ppm drop and lime dust, is that it pushes through the water
ambient CO2, which will change in the water, as it will find acids (H+), into carbonic acid (H2CO3) [water is said to be H2O, but really it is rarely and just briefly in that state
it is really more of a soup of H+ and OH- the more H+ you have the lower the pH is, the more the OH- the more alkaline it is; with an absolute very theoretical state of H2O at pH7.0, which is said to be neutral, as nutrient solution are preferred at ±pH 6.0, plenty of H+ are available]
Sidenote on RO water:
RO water, because it lacks hardness, has this swing dance between H+ and OH- like an Elvis concert, switching from side to side non stop. RO water as it buffers itself will grab nutrients out of the solution, and to some extent they will disappear and not register anymore on the ppm meter, a very weird and still unexplained phenomenon which gray headed chemists still argue over when drunk as it makes no logical sense. (briefly put, you have 0 ppm water, you add 10 ppm to it and it stills registers 0 ppm... really damn weird clusterfuck right there, some call it the water hole, like a black hole, but how it is possible for it to happen is yet unknown)
ok back on track.....
Carbonic acid H2CO3, will want to neutralize itself and likes to find calcium and magnesium to do so. Ending up with calcium carbonate (CaCO3) after ditching the two acids (H+) and so on and on... all of it is somewhat normal, we just don't want to speed things up too much as all this can happen quite fast, especially that your tank has exceptional stirring power, massive air intake and heat (which is a catalyst to chemical reactions).
[note: I've skipped some steps in the chemical action of it all, 1 not to bore you out, 2 because I only had two coffee so far and need to wake up still a bit more. But the end result is what counts]
Now we need not to over react, a slight drop of PPM (±100) can be expected as it is well within the accuracy range of PPM meters (no matter what the box claims, unless you paid 1000$+ for it)
Those slimy microbes also feed on nutrients, could they take out 100 ppm overnight? I do not know, seems quick but your water is hot and if the tank gets covered in slime overnight these little
slimetards did eat something to grow a texture... However this will be made worst over time as those slimy creep will colonize your pump and hoses and some of them might actually bad for your plants.
You do not want to be breeding pythium, fusarium or other root pathogen in your feeding lines...
Ditch the air pump, not only it is not needed, but it actually adds more problem than it does oxygen. Once that nutrient is delivered to the coco, the porosity of the medium
will provide way more aeration that the extra 1 or 2% the solution can actually hold. Massively diffusing airborn crap into your nutrient solution defeats the purpose of having a UV light on your water source too.
fact is, reducing your solution temperature will increase the soluble oxygen levels way more, but it will still be irrelevant once applied to the porous medium.
Air Pumps are part of old school (pre-internet era) myths, like peroxide and all the other crazy stuff growers used to do beforescience became available to hobbyist. Myths that are
pushed today by internet gurus who claimthat they have been trained for ages by the gods of weed or something...
Air Pumps are only essential if you are growing in deep water culture systems, but they bring the same kind of problems (microbial growth and nutrient falling off)
This is why people who do DWC, have very few successful crop in lifetime the other reason is water leaks getting them busted.
beside, the kind of plants you are growing are considered "semi-arid", so growing them in a bubbly swamp is not a great idea to begin with.
Hope this helped!
Cheers!
a little prevention goes a long way and this is my first run in coco
