[Aquatic Plant Nerd]

Hi All,

Is it ok to store KNO3 in an aluminium or tin container long-term?

[Arkcon]

Generally, we keep soluble ionic solids best in plastic or glass, to avoid metal corrosion.

[Aquatic Plant Nerd]

Hi All,

I'm currently using CaCl2 as a source of calcium for aquatic plants. CaCO3 is also commonly used as a calcium source for plants but this raises carbonate hardness which affects pH. I use CaCl2 to avoid this.

CaCl2 is known to dissolve a little better than other forms of Ca, but still doesn't dissolve very well. Is there a form of calcium that won't adversely affect water parameters (or harm livestock) that dissolves better than CaCl2?

If not, would using a mortar and pestle to grind the powder down improve solubility?

Cheers
GT.

[Arkcon]

Calcium chloride is very soluble in water, certainly at the level that plants require it.  We tend to not use calcium chloride for terrestrial plants, because it adds to the salinity of the soil.  Calcium nitrate is more soluble, but the nitrate is also a nutrient, which must be accounted for.

I hope you don't mind my merging your two disparate posts into one thread.  If you ask all your questions in one thread, we can see what you know, and what you need help with.

[Aquatic Plant Nerd]

Hi Arkcon, thanks for the help. I understood everything there.

For posterity, I have basic chemistry knowledge and need plenty of assistance!

Next question: I've had problems with fertilizer solutions spoiling. Is there a preserving agent that I could add in which is harmless to aquatic-life and won't react with the nutrients? I've seen folks use glutaraldehyde but it's quite expensive to source in Australia and dangerous to work with. Any other commonly available, relatively inexpensive options?

[Arkcon]

How does it spoil?

Solid, inorganic salts should be immune to bacterial attack.  Dilute solutions often grow microbes.  Keep kings dry and you shouldn't have problems.

Is one of your ingredients urea?  That is prone to bacterial attack when moist, you can't help that.

Are you talking about other losses, such as chemical reactions?  You should keep the components separate until use.

[Aquatic Plant Nerd]

By spoiling I mean the solutions develop mould after a while. I have a macronutrient fertilizer which is a mix of KNO3 + KH2PO4 + distilled water, and another solution for chelated micronutrients (to keep Fe and PO4 separate). After 12 weeks or so mould can develop so I toss the rest of the solution and make a new batch at that point. I'd really like to add a common/cheap preservative to extend the life of the solutions if possible and was hoping you'd have a suggestion.

I'm not using urea - it's really not the best source of nitrate for aquariums, it can lead to increased algae and some other problems. Aquatic plants take up ammonia preferentially over nitrate, so the plants love it, but it has unfortunate side effects. Some commercial fertilizer producers for aquariums (eg. Seachem) use urea because it's cheaper, but in highly diluted solutions which prevent the algae issues a little....

The losses I'm referring to are chemical reactions etc. The preservative would need be non-reactive (right word?) with KNO3, KH2PO4, K2SO4, MgSO4 and chelated micronutrients (EDTA).

[Arkcon]

Yes molding is a problem on stored inorganic salts that get moist.  The best answer is to keep them scrupulously dry.  Seal them, in plastic containers, with silica gel packets.  Use the indicating type, and replace or regenerate the silica gel pack when it turns pink.  Once dry enough, you can keep them indefinitely.

[Aquatic Plant Nerd]

To clarify Arkcon, it's the fertilizer solutions that are developing mould. I was hoping I could add something to the solutions to prevent mould or other nasties forming. Some hobbyists add a glutaraldehyde solution to the mixture which prevents mould etc but this is quite expensive. I'm hoping there's another option.

I keep the dry salts in air-tight containers and they've seemed to keep well for a few years now. I'll take your advice though and source some indicator-type silica gel packets.

[billnotgatez]

@Aquatic Plant Nerd
Has anyone in your hobby done the same process as food canning?
That protects food from spoilage due to microbes.

[Arkcon]

There are preservative that can help, but its hard to know what's compatible with your application.  Like billnotgatez:, a good solution is to work with aseptic technique -- boil the solutions of salts, and keep them in boiled glass jars, and have them open a briefly as possible.