Welcome to the blog, Shell! Sorry for the delay in answering your comment, but it's been a bit busy around these parts for the last few months. I'm so glad you want to use preservatives!
For melt & pour soap or CP soap, you don't need a preservative. The pH of these products is high enough to repel any beasties that might want to live on your soap. If you add things like goat's milk, you might need to preserve the melt & pour.
Every supplier is different, and it's hard to make a blanket statement about every base, but they should include enough preservative to handle the addition of 1% or 2% fragrance oil. If you want to add more liquids - water, aloe vera, hydrosols, milk, and so on - you will need to preserve it further. Give your supplier a call and find out what they suggest.
The suggested usage rate for liquid Germall Plus is 0.1% to 0.5%, and this should keep your product preserved for its shelf life. (I would expect any products I make today to be well preserved until next Christmas!) There is no need to use another preservative along side liquid Germall Plus as it is a broad spectrum preservative, which means it will fight yeast, bacteria, and fungi.
Citric acid can be used as a chelating ingredient and pH adjuster, but keep in mind that as little as 0.2% can alter the pH to the acidic side up to 1 level, which is a big deal. You could also use potassium sorbate at up to 0.39%
As a quick aside, please sign your anonymous posts with your name (first name only is just fine) as per my new policies about posting on the blog. It's nice to know who you are!
A few points of interest about our products, preservation, and shelf life...
- If you are using a broad spectrum preservative, you don't need to use another preservative. You can add a chelating ingredient like citric acid or EDTA or an anti-oxidant like Vitamin E, but you don't need to double up on the preserving power.
- If you aren't using a broad spectrum preservative, make sure you are combining them so the preservative can combat yeast, bacteria, and fungi.
- The shelf life of your product is the shelf life of the shortest lived product. If you are using something like grapeseed oil, the life span will be 3 months. If you are using something like shea butter, you could have a life span of up to two years.
- You don't need to preserve an anhydrous (waterless) product unless the product will come into contact with water, like a sugar or salt scrub. You can add an anti-oxidant to extend the life span, something like Vitamin E, which also offers some skin softening properties.
Preservatives - an entire section on the blog
Shelf life of your products - scroll down to find the four posts.
Water activity and scrubs