I would definitely agree that some heat in the water will help. Cold water doesn't help the detergent get going properly so even heating the water a little should help.
Synthetics can trap nasties because of the structure of the fibres - whether that is too much detergent or too little meaning that dirt is left behind. I'm yet to be convinced that hard water deposits are a bigger problem than either of those! Cold rinsing will not leave mineral deposits behind, only heated water will really do that. I'd just wash any smelly nappies with a full dose of detergent and lots of water, rinsing until all the detergent is gone. Sometimes it can help to use a different detergent to your usual one, same as switching shampoos can be good sometimes. You can use cloth or normal detergents; it is absolutely not true that nappy companies only make them to make money as some people want to believe.
After you've cleaned out any gunk, wash with whatever dose of detergent you're comfortable with. If that's a full dose, go for it. If you want to keep it down, maybe go for 1/4 or 1/3 dose (start with a full dose if it's cloth detergent). Sniff them when they come out - if they've not been washed properly you'll know! If that's the case, put them straight back in and rewash with more detergent. If they're still smelling of detergent, that is a clear indicator that there is still detergent in your nappies. "Designed to rinse clean" is not true of most brands. Optical brighteners are designed to stay in fabrics to help them reflect light better (makes them look sparkly white!), fragrance is designed to be left on fabrics so you think how wonderfully clean your stuff is. Some machines are simply better at rinsing than others! Mine is terrible - great wash but poor rinsing = not much detergent needed but extra rinses are.
You can get little testing strips for water hardness - one came with the dishwasher when we bought that or I think you can just buy them cheaply online. Or look up your water company and they probably have something telling you - here they call it a water quality report. You might need to scan through a few pages of stuff about what bugs they found in the water and water hardness will just be a little bit with it given in a few different measurements. You can normally tell if you have hard water though - do you get white scaly bits in your kettle that fall off and ruin your tea after a while? If you go away from your area, do you need more or less shampoo to get the same bubbles on your hair? If you need a lot to bubble up (taking into account how much hair you have and how dirty it was), you probably have harder water.
I realize that you and I differ with pretty much everything in terms of CD, but I will post a response for anyone who would like the information.
Cold water is fine to use if a person is using a strong, mainstream detergent, but not a plant based one, as they requires hot water to work effectively. Strong mainstream detergents would be detergents such as Tide, Gain, etc., here in Canada; people can search out comparable brands in their own countries if interested.
Hard water minerals are present regardless of the temperature of the water. Not quite sure where you have found info to the contrary... ? An easy way to prove this would be to do a water strip test in cold water.
Optical brighteners will not effect the efficacy of diaper absorbancy, nor will they make them smell. They are a non issue in terms of CD. As are enzymes, which essentially attack poop and bacteria.
Unfortunately, washing with too little detergent may not make issues arise immediately, but can do so overtime. Detergent dosage shouldn't be some exact science as most people have diaper loads of various sizes from time to time, which may require more or less water/detergent but not so much so that it seems daunting to try to figure out.
To use myself as an example, I always use the scooper provided in the box and scoop to line 1 for my prerinse regardless of the amount of nappies washed (generally 12-16 w/ 1 insert each and maybe a wet bag) and to line 2 in the main wash with 2 tbsp calgon for up to 18 nappies with 1 insert each max. That's it, simple and easy. An extra rinse at the end of the main cycle and that is it. We have hard to extremely hard water here and I use a front loading machine.
If anyone is using a fragrance detergent, I'm not so sure they are worried about fragrance, and truly, as long as they don't feel soapy or slimy, there is truly no need to rinse until all detergent smell is gone. This poster may not believe hard water exists
but it does. If you have hard water and you are rinsing like mad because of some light smell of detergent, it truly will work against you and redeposit those minerals onto your diapers, regardless of temperature.
Of course anyone is free to use whatever they want to clean their diapers, and however much, but I strongly suggest you consider your detergent kind as well as the amount used if you consistently encounter issues of any kind.
