How would you modify a Holtrefeter's Solution to accommodate plants?

[Elise]

I'm curious what components would need to be added to a Holtrefeter's Solution to support live plants? Would Magnesium Sulfate (MgSO4), Iron Sulfate (FeSO4), and Manganese Sulfate (MnSO4) be correct?

For reference here is the components currently in the solution:

Holtrefeter's Solution
NaCl......................Sodium Chloride
KCl.......................Potassium Chloride
CaCl2.....................Calcium Chloride
NaHCO3....................Sodium Bicarbonate

 

[Jennewt]

It's hard to advise without knowing what you are trying to accomplish overall... axolotls in a planted tank? What concentration of Holtfreters are you planning to use - people use it at various diluted strengths. Would it perhaps work better to use plant food rather than adding things to the Holtfreters?

 

[Elise]

I would be adding plants to an axolotl tank, yes. I'm stuck using RO/DI water and would be using a Holtfreter's solution to harden the water.

Would it perhaps work better to use plant food rather than adding things to the Holtfreter's?

At first it seemed tautological, but I understand what you are saying now and this may be my solution. However, what I'm concerned with is most plant food has calcium and potassium as their main ingredients, and as this is the same with Holtfreter's, it would cause the water hardness to increase. It might be a small increase and it might be easy to adjust for, but I haven't tried anything like this yet.

My initial thought was since I would be mixing a solution already, I could just add a few more missing macro nutrients to my solution to achieve the same results as plant food (not including trace minerals which I'm not worried about).

 

[oceanblue]

I use a modified Holtfreter's solution made up with very soft tap water or on occasion water from a dehumidifier, (essentially distilled) using a total salts level of about 1.25 g/L. (For comparison blood is about 9g/L and seawater 35g/L) The axolotls waste seems to be adequate fertiliser although I occasionally use an iron chelate based plant fertiliser if they look a bit pale. If you take the salt level higher some plants will not thrive.

Picking up points in your other thread about salts, Chloride is an important component involved in ion transport across gills, do not try totally substituting sulfate. Sulfate is less important, sulfur compounds in food probably meet all needs.

Another problem with sulfates is the low solubility of calcium sulfate.

I currently use a stock solution of 25ml per final litre of water containing in each litre:
Calcium chloride 4g
Sodium Chloride 40g
Potassium Chloride 3g
Magnesium Chloride (as dihydrate) 10g

The calcium chloride is standard "dehumidifier granules" grade, the salt ordinary table salt and I use 4g of Lo salt, a 66% potassium chloride table salt substitute instead of pure KCL
I used to use magnesium sulfate at the same weight as MgCl but if you do make sure everything else is dissolved before adding it or you will get calcium sulfate formation around your calcium chloride and this very soluble salt will stay as lumps!

If you try making a stronger solution with sulfate you will find crystal needles will form, Its why I've changed to the chloride and I'm working on a stronger stock solution.

With me the mix produces a final pH of about 6.8 but despite that lime loving watercress thrives in it.

 

[Elise]

Very good. MgCl is used in a large portion of your solution. What made you choose to add so much? Also, are you not using Sodium Bicarbonate or is it added after you mix your solution?

 

[Elise]

Answered my own question.

Indiana University Axolotl Colony use a modified Holtfreter's solution which leaves out the NaHCO3 and uses MgSO4 in the same weight.