Alright, you've finally saved up enough cash to get yourself some waterblocks and the like, only to not stop and consider the consequences of what you're putting in it. This is a small guide quickly covering the most important things you need to take into account when making a custom loop.
PC liquid cooling has always required contact with raw metals. Copper, aluminium, silver, nickel, and brass are all common in this work and react differently (possibly violently) together. So what is the final word? Don't mix metals. I personally recommend sticking to copper. It transfers heat best and plays fine with brass (fittings) and silver can be used as a biocide. If you buy nickle coated blocks, you need an anti-corrosive agent as well as a biocide other than silver. Using silver as a biocide can void your warranties with some companies. Aluminum corrodes very badly with copper when they are electrically connected through water. Mixing these two is a big no-no and in general aluminium is only used in poor quality radiators and fittings; stay away from it.
"What water do I use?"
"But... some guides say bottled because..."
"What about for cleaning out..."
Bottom line, the only liquid components that should ever touch the inside of your blocks are: Distilled water, 99% alcohol, water wetters, biocides/algecides, and dyes (at own risk).
Always buy premixed or make sure to mix OUTSIDE the loop.
Never EVER use FOOD COLORING or anything with any sort of glucide component. Glucides are sugar, sugar is food that will turn into gunk and later bacterial growth.
All dyes carry the risk of discoloring tubing, clear blocks, and non-glass reservoirs.
A way to combat this is by draining your dyed coolant every 3-6 months and running a 50/50 99% alcohol and distilled mix in your loop for no longer than 2 hours, waiting an hour for the alcohol to evaporate before refilling.
On the topic of additives, everything you add to your water makes it perform WORSE. Almost...
The only exception is a water wetter, when used in small amounts (about a 95% water, 5% percent wetter mix [depending on concentrate]) you can slightly enhance the performance of distilled water beyond that of its own. I've only tried this with a brand called hy-per lube. hy-per lube also boasts anti-corrosive properties, which distilled water NEEDS speaking of corrosion...
Distilled water is often considered the best and ONLY thing you should be running in a PC loop and for the most part its true. The thing about distilled water is that it is a rather low PH, around 6. The problem is that because it's had all its minerals (ions) removed, distilled water becomes ionically hungry. This is like an acidity to metal, and needs to be combated. In order to cure the innate corrosive properties of distilled water, you need to up its PH anywhere from 8-10. How you do this is up to you, although some water hardeners do have glucides which can act as food for bacterial growth. Avoid glucides at all cost.
As already mentioned, the final component of proper water chemistry is your biocidal and algecidal treatment.
Over time your loop if left unchecked will begin to host bacteria and alge, which will gunk out your blocks and water pathways.
Now, depending on your block type and manufacturer policy you won't be able to use one of the cheapest and most effective methods.
Silver kill coils or any piece of 99% pure regular silver will keep your loop clean and clear due to its natural biocidal properties. However, it is known to react badly with nickel, which is why its used less and less with high-end loops due to EK's nicer blocks being nickel plated.
in this case, I would recommend running EK's own coolant and PT nuke for additional protection.
PT nuke is a very effective additive for loops that will react with silver.
Alright, that's all I've got for now. Will edit in any additional advice you guys have that belongs. Happy looping, build it beautiful.