Does magnesium sulfate in aqueous solution form magnesium (hydrogen-)carbonate when hydrogen carbonat is present? I'm using an additive of magnesium sulfate to complement my fertilizer. The additive lists the following ingredients:

I know that it does NOT contain magnesium oxide, because due to historical / commercial reasons ingredients of phosphorus, potassium or magnesium are indicated as mass percentages of the oxides with the element in question. Also the merchant confirmed that the source of magnesium is magnesium sulfate.
I noticed the precipitation of a white powder at the bottom of my reservoir. I suspect it to be magnesium carbonate. The  mains water contains the following chemicals. The dose of magnesium sulfate is within the range recommended. The precipitation occurs even if I do NOT use any fertilizer, so I think It is a reaction with chemicals in mains water supply.


Is the precipitate magnesium carbonate?
How can I prevent this precipitation? What are factors influencing it besides the availability of hydrogen carbonate?
EDIT:
User AJKOER suggested that the precipitate is calcium sulfate. I don't think that is the case because:

The solubility of calcium sulfate is given at 2.1g / liter @ 20° C  (https://en.wikipedia.org/wiki/Calcium_sulfate). This equates to about 2.1 * 0.71 ~ 1.48g sulfates per liter. (mass of SO4 /  mass of CaSO4 = 0.71)
I'm adding only about 92.1 mg / liter sulfates from magnesium sulfates
The mains water contains only 13.3mg / liter sulfates
92.1 mg / liter + 13.3mg / liter &lt;&lt;&lt;&lt; 1480 mg / liter
The white precipitate is more likely insoluble white calcium sulfate.
Per a reference on the making of fertilizer, to quote:

Calcium, magnesium, and sulfur are also important materials in plant growth. They are only included in fertilizers in small amounts...

Net ionic reaction:
$\ce{ Ca^2+ (aq) + SO4^2- (aq) -&gt; CaSO4 (s) }$