DI water, pH, TDS, fertilizer, KOH, ProTekt, TRIS? - Page 2 - Orchid Board

tropterrarium · #11 07-13-2011, 02:13 AM

Did some trials, and it takes 1.3 ml of 1N KOH per 1 gal of DI to get pH from <4 to ~6.5. Quite a bit more than I would have guessed.
Next step is to automate it, specifically for a holding reservoir I use. The content is turned over usually in a couple of days, so have no worries about long term drift. I have a HerpKeeper unit running for misting and temperature control, will add a pH probe to it that will trigger a dosing pump with KOH, and add a circulating pump to the reservoir. So that should keep the stock and misting water in good pH, so only will have to check for fertilizer drift.

For dosing pumps I consider either a cheap e-bay peristaltic pump, the LiteMeter III supplemental pump (also peristaltic), or a Hanna Instruments BL series with piston drive. The last one may be the most durable, and is rated for KOH. The Litemeter is supposedly very reliable, and works on low DC voltage, which is nice.

Re fertilizer, the firstray pure water MSU fertilizer is VERY unbalanced with NPK of 3/0.75/4 in liquid form, and 13/3/15 in powder form. Dynagro is 7-9-5 and has additionally cobalt in it. I may be tempted to balance the Dynagro pH drop with either Protekt or a dash of KOH. The K addition will make the Dynagro formula even more balanced, a nice side effect.

The Technaflora also has fewer micronutrients, so rather stick with the Dynagrow. It never produced any precipitation when mixed with any water I have used it with, so seems to have a pretty stable formula.

Fun little project!

Ray · #12 07-13-2011, 09:34 AM

I think your DI water is not as pure as you think.

Pure water has a neutral pH, but upon absorption of CO2 fro the air, it will acidify. The pH of the solution is controlled by the concentration of the CO2 in the air, and as that is a more-or-less constant, the equilibrium pH should be about 5.4. The fact that yours was 4 suggests there are additional acidic species still in solution - which could explain the relative degree of buffering that forced that "large" KOH addition for adjustment.

Ray · #13 07-13-2011, 09:40 AM

Quote:

Originally Posted by tropterrarium

Re fertilizer, the firstray pure water MSU fertilizer is VERY unbalanced with NPK of 3/0.75/4 in liquid form, and 13/3/15 in powder form. Dynagro is 7-9-5 and has additionally cobalt in it. I may be tempted to balance the Dynagro pH drop with either Protekt or a dash of KOH. The K addition will make the Dynagro formula even more balanced, a nice side effect.

What are you trying to say here?

Do you mean the formula is unbalanced, as in not 10-10-10? If so, be aware the MSU fertilizer was formulated that way specifically, as it most-closely matches all of the plants' needs, based upon a thorough study compilation of orchid tissue and ash studies. Additional minerals in a "balanced" fertilizer are wasted.

tropterrarium · #14 07-14-2011, 12:09 AM

Hi Ray,

Re pure water, point well taken. Carbonate species will acidify, and I live in an urban area, so all sorts of gasses like SOx, NOx, will have additional effects. DI is not Sigma water purchased in bottle; that's what I've used for setting up PCR reactions. Whole different animal.

You are interpreting my response correctly. Re ash study, this is a long-term time-averaging approach, but living organisms are not machines. Some times they need more of one, some times more of the other. These needs can easily change during a single day. And excess is not used. OK, I may waste some chemicals, but at least I am not keeping supply artificially low either. Performance is limited by the nutrients in shortest supply, regardless of availability of the remainder nutrients. That's also standard plant physiology. Last but not least, it seems that precise composition of fertilizer (except for low urea: important for me as I grow predominantly on mounts) is not that critical. The old switch from grow to bloom formula etc. does not seem to hold any water. So I will get something locally, save on shipping.

OK, experimented further. TDS of pure DI = 0. TDS of pH~6.5 adjusted DI = 20. Added 1/2 tbsp of fertilizer (Dynagro 7-9-5) and pH of pre-adjusted water dropped to pH~5 with TDS at 459, had to add about 1.5 ml 1 N KOH to get it back to pH~6.5, TDS at 539.

The TDS values after adding fertilizer seem very high. MSU lists TDS 260 for what I added. It may be that the liquid base has evaporated quite a bit and the remainder is much more concentrated. I am at the end of the bottle, which is about 5 years old. MSU also recommends to keep total TDS <350. Although not specified, I take that a once a week fertilization is assumed. As I water with very low TDS water (20), I should be safe with TDS of 300 for water with fertilizer. So will possibly use the remainder Dynagro on some non-critical plants (grow some CA natives on an outside bench), and get a new supply of Dynagro.

I decided not to fiddle with TRIS. Rather keep the variables to the minimum. Is complex enough already.

pH probe, SL1 for HerpKeeper, plus dosing pump (LiteMeter III) and a circulating pump are on order. Should be fun setting it all up.

Ray · #15 07-14-2011, 10:46 AM

Quote:

Originally Posted by tropterrarium

You are interpreting my response correctly. Re ash study, this is a long-term time-averaging approach, but living organisms are not machines. Some times they need more of one, some times more of the other. These needs can easily change during a single day. And excess is not used. OK, I may waste some chemicals, but at least I am not keeping supply artificially low either. Performance is limited by the nutrients in shortest supply, regardless of availability of the remainder nutrients. That's also standard plant physiology. Last but not least, it seems that precise composition of fertilizer (except for low urea: important for me as I grow predominantly on mounts) is not that critical. The old switch from grow to bloom formula etc. does not seem to hold any water. So I will get something locally, save on shipping.

I cannot argue about a single point, but I doubt that anyone - using any complete fertilizer formula - ever ends up with a nutrient deficiency issue. Compared to the availability in nature, the amount of nutrition we provide is overwhelmingly greater - especially if we feed frequently.

Plus, plants have "nutrient pumps" for some elements, taking it up and storing it, even if it's well beyond what they need. Phosphorus and boron fall in that category, I believe, but I'm sure there are more.

tropterrarium · #16 07-14-2011, 01:06 PM

All nutrients are taken up by active pumps, seven loop transmembrane protein channels usually, only water goes in and out by diffusion/osmosis. The one exception may be in extreme stress, near death, when the pumps fail. Then it becomes a diffusion process from high concentration (plant tissue) to low concentration (environment). But a pump cannot transport something that is not there.

You are quite right, that precise formulation does not matter that much. I would argue the most important thing is a rich diet, so as many different trace elements as possible. The idea of rotating various fertilizers seems appealing to a certain degree, though not sure it is worth the additional complication. And somehow proper pH, so that the plants can access the nutrients.

tropterrarium · #17 08-01-2011, 02:19 AM

For those of you interested in pH adjustments, here is my solution:
I have an intermediate storage of DI of about 20 gals, that is filled automatically with a float valve. The water is actively circulated with a small aquarium pump (Rio 180 powerhead). pH is monitored with a pH probe from DigitalAquatics, connected to a HerpKeeper controller through an SL1 unit. I have a 1 gal reservoir with 1N KOH, and a dosing pump (SpectraPure® LiterMeter 3 Remote Pump Module (LM3-RPM)) that pumps the KOH into the reservoir. I chose this model, as it gets good reviews with respect to reliability, but does not have any timer/controller extras, which I don't need. Additionally, it runs on 12V, so electrical hazard is very low.
The LM3-RPM runs nominally at 12V DC, so to reduce pumping capacity I put it at 6V (4.5V is too low to do anything).

The HerpKeeper is programmed as follows: One of the powerstrip (PC4) outlets has a timer function: 2 seconds on, then 1 h off, as a continuous loop. Additionally, there is an alarm associated with the outlet, which prevents the outlet to turn on if pH>6.25.
Result: the HerpKeeper checks every hour, if pH is below 6.25, if so, then the dosing pump turns on for 2 seconds. That delivers about 5-6 ml of 1N KOH to the 20 gal reservoir, the Rio pump mixes everything, and then pH is in the 6.35-6.4 range.

Works like a charm, fully automated and in reasonably tight pH range.