All modern dishwasher detergents are formulated to work specifically in dishwashers. On no occasion should ordinary washing up liquid be used, as it will cause excess foam, which can result in a leak. If it is accidentally used, sprinkle ordinary salt into the chamber to disperse the resulting suds. Then rinse away the excess salt before using.
There are 3 main types of dishwasher detergent - Powder, liquid (or gel) and tablets. Which one you choose will be down to personal preference, but most people find tablets very convenient, although using powder is usually more economical and liquids are less abrasive on more delicate items.
Most dishwasher detergents contain phosphates and are necessary to ensure an efficient clean, although from January 2017 will contain much lower doses because of EU regulations. Some people like to make their own dishwasher powder recipes using traditional cleaning products, but the general advice is to use dedicated products that have been formulated with an optimal mix of ingredients. There is an argument that there is an overwhelming choice of products on the retailers' shelves, making increasingly bolder claims, but you'll probably find that they all have similar performance so you may as well buy what's on offer at the time. You'll still get the best results by ensuring you use a rinse aid and dishwasher salt.
Which cleaning products to use?
As the number of dishwasher owners grew, the number of products available multipled; first with 'Dual action' products that contained a rinse aid, and then '3-in-1 tablets' that also contain an ingredient, which has a 'salt action' to soften the water. Fast forward to today and there are products claiming '12 x actions'. The reality is that much of these claims are for marketing purposes. However, the general rule is that no matter what claims the detergent manufacturers make, you will still get the best results from using separate rinse aid and dishwasher salt - just as separate shampoo & conditioner gives better results than 2 in 1 hair shampoos.
The salt action takes place in the cleaning chamber of the machine, but does not actually replenish the water softener. Research has shown that whilst detergents with 'salt action' do clean dishes effectively, their performance is improved by adding salt to the water softener reservoir, in all but the softest water. Be aware that if you have not been filling the salt reservoir and relying on the salt in multi-function tablets, then it may take a few cycles to re-generate the softener.
As the performance of machines can vary, as can local water conditions, it is always best to follow your dishwasher manufacturer’s advice.