I have very hard water too, but never heard of using baking soda. I use 20 Mule Team Borax, a scant tablespoon along with Biokleen laundry powder. My machine is small -- an Asko European-sized -- and I do small loads, so a tblsp. of each is all I need. The Asko manual suggests adding 1 oz of citric acid into the wash drum and running a 205 degree program to remove deposits that may form on the wash drum. I've never had to do this.

Baking soda can make hard water "harder". Depending on where you are in the country you may already have a high level of bicarbs in your water. Borax would be a better choice.

I work at a hotel that had way too much stained laundry the stains were set in nothing work we couldn't afford new laundry during the out break. I took Persil ProClean and filled a big sink of hot water mixed baking soda in with it then took and poured vinegar let it soak a hour then put them in washer added all three things and I got out just about all the stains out.just a few sheets and towels still had stains. The laundry did not have no vinegar smell, it saved the hotel a lot of money. I now use the same things on my baby grandson stained clothe

German Persil leaves zero film and zero scale. Be it liquid, powder, or pearls. I have used German Persil for years until recently. I feel it is too concentrated and harder to dose in the Miele W1. I am now using the Miele powdered detergent for colors and whites. Dosage recommendation on the box is working well. Although for certain things I reduce amount.

Note that if you do a clean cycle, citric acid such as Finish Booster for dishwashers works well. 2tbsp in drum. Your machine will sparkle inside after. For hard water I would descale every 6mos.

@Crystalannj Johnson, I honestly do not understand where this internet misinformation came from but Vinegar does not remove stains, or improve the performance of a Soaking or Wash Solution. I will say, it will remove certain rust stains, but beyond that, you are neutralizing Detergent instead of increasing performance by adding it.

Baking Soda, on the other hand does improve performance, but it's so minimal it's not really worth adding. Borax would be a much stronger additive and better product, if someone was trying to remove Odors.

Lastly, mixing Baking Soda & Vinegar doesn't accomplish literally anything. You are just watching the effects of two chemical agents, neutralize each other.

If you were going to do this again, I would suggest just using the Persil Alone, or adding something like OxiClean or Biz Laundry Booster instead of Baking Soda.

And whatever you do, do not Soak Clothes in Chlorine Bleach for extended periods of time.

Lastly, for the OP (who I doubt is around after 8 years) -- Baking Soda is a Water Softener, but a very poor one. You are far better off adding additional detergent, using STPP, or getting a whole home water softener.