My chelated stock solutions should include ascorbic acid at recommended levels (I’m intending to make up with distilled water) to prevent precipitates but do not need potassium sorbate if kept in the fridge, and should last indefinitely. This would include the Cu 15% EDTA that I’m planning to use?
That’s correct, I would add the Ascorbic to the larger volume of distilled water and dispense this for your solutions rather than for each sample so you don’t have to measure small weights each time.
‘Unchelated stock solutions may or may not require acid depending on the compound’. I think the only unchelated compound I’m looking to make up as a stock will be Mo (NH4) so can you confirm if this requires the acid or not?
It’s probably not necessary to acidify this solution but you can always use the acidified stock distilled water first and see if there’s any precipitative reaction, I use Sodium Molybdate and that forms a stable solution without acidification, your not going to waste much salt trying it out if it doesn’t work.
Once made up into the final mixed dosing solution, ascorbic acid and potassium sorbate should be added at the recommended level for the full volume, if the intent is to store the solution at room temp (I.e in the tank cabinet for easy access) The micro solution would include a mix of both chelated and unchelated compounds so the acid will prevent precipates and the potassium sorbate will preserve.
No need to add any more Ascorbic Acid if your stock distilled water is already acidified beforehand. You only need to add the Sorbate if the solution is stored/used in a warm area away from refrigeration.
The Macro solution is KN03, KH2PO4 and K2S04, none of which are chelated (and clearly I don’t need stock solutions) so this would just need the potassium sorbate for preservation and no acid as these are not chelated compounds?
No acidification required, preservative is optional, a Macro solution containing potassium salts only is unlikely to be a breeding ground for much unless the distilled water source is not fully pure and contains micro elements in the parts per billion/trillion (enough to feed a fungal or bacterial colony).
….other than magnesium, which I was just planning on dosing dry once per week after water change.
This is fine it just makes this a remineralising strategy for waterchange rather than a dosing strategy mid week.
I’m guessing that the world wouldn’t end if I just used both the preservative and the acid in everything but as a first step into DIY salts it’s good to have that basic understanding of how things interact. 😊
This is Ok to do as long as you don’t have any precipitate formation, as I said above Acidifying the distilled water source first before distribution between the compounds you want to solve makes the process easier and saves on weighing multiple small amounts and reduces the risk of using too much Ascorbic to shift the pH, using the minimal amount I mentioned in a post above to obtain a pH below 4 (depending on the source water pH 3.2 @ 0.5g/L for 0TDS RO/DI) is all you need, if you want to shift the pH one point lower it will take 10x the weight of acid you initially added, extra stuff not needed but free to participate in precipitation reactions.
🙂
