For me, I have been keeping CRS in warm temperatures of 26-29°C without a problem and they have even bred a lot for me. Many people think that CRS are very, very sensitive shrimp but they are quite hardy. I think that they can slowly adapt to the warm temperature and get use to it. So I´m going to give some tips on how to keep CRS in warmer temperatures.
First of all, if you want to keep your CRS in warm temperatures, most important is that you need very clean water. You can just get a canister filter (Eheim is a good brand to choose) and do water changes regularly, then that shouldn't be a problem.
Secondly, your pH have to preferably be low. Optimum pH is 6.2 - 6.8, but I´ve kept my CRS at pH of 7.5 before and they have still bred for me

Third, you need a decent sized fan to blow on your tank to reduce the temperature a little. With a fan I managed to get to only 27-28°C.
Further, feed your shrimps more vegetable-based food such as spinach, bulberry leaves etc. This can help with your shrimps coloring. Of course adding some MOSURA Mineral Plus also will help a bit.
Or what you can also do is: make your own DIY manual chiller.
It managed to bring my temperature down to about 25-26°C for the whole day.
This is how the "chiller" looks like:

Inside the "chiller":

If you want to make this, you will need the following things:
- Canister filter
- Styrofoam box suitable in size to fit your canister
- many 1.5 or 2 litre bottles
Alright, first you just have to cut a small hole that can just fit the tubes of your canister (refer to picture 1). Next, put your canister into the styrofoam box and put some water into the box. The water level should be about 3-4 inches high. After that, just fill many 1.5 litre or 2 litre bottles with water, put them in the freezer and let the water inside turn into ice. Then just put the bottles of ice into your box every day. The ice won´t melt that fast due to the styrofoam box and the water in the styrofoam box is cooled to a lower temperature by the ice. The water keeps flowing through the canister filter and will also be cooled down, so your tank water can also be cooled.
Once it's finished, it will look something like this:

Thanks!
Here are some pictures of my shrimps to share:





