Did you read the label on your borax cleaner? Did it contain anything else such as chlorine or parabens?
Ordinary borax(sodium tetraborate) is very safe according to its Material Safety Data Sheet(MSDS) - borax is about as poisonous as ordinary table salt.
You could also use boron tablets from a health shop -- these will be expensive -- but these are given in tablet dosages of only 3 -- 6 mgs and you will need much more than that to kill the candida. In proper dosages, Borax also helps to balance the hormones, stops and reverses osteoporosis and arthritis and helps to remove fluoride safely from the body(fluoride is an acidifying root cause of candida). See this link on arthritis:
I also know people who just use the 20 Mule Team Borax for the remedy. This is a very cheap form of borax and it is effective.
You candida problem is not due to candida becoming "resistant". The reason your candida always comesback after a while is probably because you have had candida biofilms for years or decades and you aren't taking any direct protocols to remove these biofilms. Candida biofilms(where candida safely hides) are like impenetrable fortresses where anti-fugnals and the immune system cannot penetrate to kill the candida. So the candida always survives and keeps coming back no matter what you supplement. To get rid of the biofims for good take the turpentine remedy that I recommend in my protocol. Read this. You will also need to take iodine, borax, alkalize etc so that you also use multi-protocols to kill the candida when you remove these biofilms. Using multi-protocols will confuse tye candida and you will get much better results.
Take borax for four days on three days off if you wish. Borax is very efficient at killing both candida and parasites. Borax also kills mycoplasma and helps to get rid of fluoride from the body as well.
I would recommend you take the following with meals if you want good liver protection:
Milk Thistle -- 450 mgs twice a day
ALA -- 300 mgs to 600 mgs twice a day
Selenium - 200 micrograms twice a day
Magnesium Citrate -- 500 mgs twice a day -- neutralizes poisonous candida alcohol toxins.
Molybdenum -- Neutralizes poisonous candida aldehyde toxins. Molybdenum also kills candida.
The above acts purely as protection for the liver against candida poisons.