Acidic MSU-RO Solution Precipitates

[jmrathbun]

Following recommendations from this forum, I recently mixed a pound of MSU-RO fertilizer with a gallon of RO water (pH 6.8) and got a very intensely green solution with a pH of 3.5 and about 5 mm of whitish precipitate that sinks to the bottom and will not go into solution. Is this normal? I'm concerned that whatever is not in solution might be an essential nutrient, or harmful to my plants when I get close to the bottom of the jug. If I neutralize this solution, will that make things better or worse? It sinks so fast that agitating the bottle before pouring won't solve the problem.

[estación seca]

Bump.

[Roberta]

Try adding more water... (like maybe another half gallon) That is very, very concentrated. You may have exceeded the solubility of some of the components.(You could also warm it up a bit... solubility increases in warm water) I assume that you have done this to use with an injector that dilutes the solution 1:100 when applied. You DO need to make a 1:100 dilution to get this soup to the correct concentration for the plants. whether you do it with an injector or some other way. (The typical Hozon proportioner does 1:15 and this is MUCH too concentrated to use that way, if that is what you have you need to dilute the concentrated stock soution 1:7 before using the Hozon) The final solution to apply to your plants should be the equivalent of about 1/2 teaspoon (at most 1 teaspoon) to a gallon! Don't mess with the pH - at the correct concentration, the pH with RO water will be what it should be for optimum benefit.

[jmrathbun]

Now I'm REALLY confused! Please see previous discussion:
Fertilizer In Solution vs Dry Mix

[Ray]

My guess is that it is mostly calcium, which may-, or may not go back into solution if diluted further, but I think that's your best option, especially if you can heat it.

The manufacturer claims that 2#/gallon is the solubility limit when using hot water, but that may be too unstable of a solution once cooled.

Don't let the pH bother you, as that is as much provided by the citric acid that is added to enhance solubility, as anything else. Citric acid is another weak acid, so whatever is happening in the pot will overwhelm it.

Don't forget: the pH of the applied solution is of far less concern than is the pH in the pot, which is best determined using the pour-through test.

[jmrathbun]

I guess if it's only calcium species, which is certainly what it looks like, I won't miss it since I'm using mostly Orchiata which is calcium heavy to begin with. I don't have a convenient two-gallon container, nor a good way to heat this one.

Are we still agreed on 1 oz concentrate per gallon of applied solution? I saw a different opinion earlier in this thread.

[Ray]

Fill your sink with very hot water, and just immerse the jug to heat the solution. Then shake the hell out of it to disperse the sediment.

One pound per gallon, dispensed at one ounce per gallon, will result in about 125 ppm N in the applied solution. I would recommend that if you only feed once every three or four weeks.

Personally, I'd go with one teaspoon per gallon - about 20 ppm N - used at every watering.

[jmrathbun]

Thanks for info!

[Orchid Whisperer]

jmrathbun:

Looking at the ingredients (second image in your original post), I see that some nutrients are supplied as nitrates, some as sulfates. A couple thing could be happening.
(1) often, when mixing nitrates and sulfates in one solution, a precipitate will form and drop out of solution. The precipitate is often a sulfate (could be calcium sulfate(?)).
(2) as Roberta said, try adding more water (because you may have exceeded the solubility of one or more of the chemicals in the fertilizer blend). you can get a general idea of the solubility of various fertilizer components here: Fertilizer Solubility - Dissolve a Fertilizer. I think adding more water will likely fix the problem.

Note: Increasing the temperature may not always increase solubility. For example, calcium sulfate will dissolve better up to about warm tap water temperature (about 30 C), but with increasing temperature above that, solubility flattens or decreases. Some of the fertilizer chemicals listed on your label do the same thing.

[Ray]

I spoke to the producer, and he thinks it is likely calcium phosphate. Citric acid is added to calcium-containing formulas to aid in solubility (which can increase by a factor of about 10 for each 1 unit of pH reduction), but they limit it in fertilizers intended for RO water, because it pushes the solution pH lower, and folks freak out over it.