Ask Erik - Recirculating Help
Erik,
I grow in a recirculating hydroponic system. It is flood-and-drain and each table has its own large reservoir. The tables hold containers filled with grow rocks. I have always done pretty well with this setup. I experiment with different nutrient programs and have tried just about everybody's line of nutrient products. Recently I started to use a line of specialty nutrients and am experiencing some issues I had not encountered before. The plants are in late vegetative state and looking very healthy. The thing that is freaking me out a bit is that the pH seems to be swinging a lot. I have a top-quality digital pH tester that calibrates to pH 6.9, so I know that it is accurate. I am using a vitamin supplement, enzyme product, and a premium specialized two-part nutrient system. I will be adding a couple of different bloom boosters at different intervals and rates. According to the label, the two-part contains a pretty wide array of chelated trace elements. To get to the point, do you think this will cause a problem for me in terms of my final yields, crop health, etc? Any idea what might be causing this?
Thanks for your question. I have encountered this before, and perhaps the situation I am familiar with mirrors yours. Most conventional premium-quality liquid nutrient systems, particularly three-part nutrients, are pH buffered to give you a stable pH in the reservoir. Now, is this an advantage or disadvantage? From where I stand it's a case of "six in one hand, half a dozen in the other." Different elements have different levels of availability at different pH levels. The same is likely true for vitamins and other growth promotants contained in nutrient supplements. To further fan the flames, some speciality nutrient programs use a very wide range of products, though perhaps not all applied at the same time or concentration.
In using more supplements, the grower needs to manage the overall
concentration (ppm or EC) of the nutrient solution. With every product
added the TDS will increase. When using multiple additives along with
your base nutrient excessive TDS levels can quickly be reached. Partly
because of this, some manufacturers will omit pH buffers in their
nutrients. The buffers such as potassium carbonate are relatively
unavailable, and generally their sole purpose is to help stabilize the
pH. So, by omitting these buffers there is more room for other elements
that may be beneficial to the crop before excessive TDS levels are
reached. Because your specialty nutrients have omitted some buffering,
you are seeing pH values change as different elements are absorbed by
the crop. As long as the pH fluctuations are gradual and swing either
one way or the other, as opposed to intermittently up and down, things
should go well. For example, if you start your nutrient off at pH 6.3
and it continues to shift gradually to pH 5.8 over the course of a few
days, your crop will have experienced a range of availability for all of
the nutrients and other beneficials contained in your nutrient solution.
In nature, the soil chemistry experiences wide swings on pH, helping to
plants to absorb a range of nutrients. Provided that the range does not
dip below pH 5.5 or above pH 6.5 your crop should do very well. Also
remember that many nutrients are supplied in several chelated forms,
some working better at higher pH levels, others working better at lower
pH values. For example, Fe EDTA works better at more acidic levels,
while Fe DTPA works better at slightly higher pH levels. If your crop
appears healthy and is showing no signs of deficiency, there is probably
no cause for alarm. Hope this helps, and I wish you much success in your
endeavour(s).
Highest Regards,
Erik Biksa