That's the same brakes (Promax Solve) that my son's GT mountain bike has. I'm about to perform some maintenance on it in a day or two. The front brake needs to be burped, which is typical of all hydraulic brakes.

The problem is finding information from Promax on using the fluid. It uses mineral oil, but the online site states to only use Promax mineral oil. I can't find it anywhere.

So I'm planning on using the mineral oil for my Tektro brakes to burp his brakes.

I've also had to replace the pads on his brakes, they use the same pads as Shimano and Tektro Auriga's.

Clarks Organic Disc Brakes Pads for Shimano Deore/Auriga Comp/Aquila/Clarks S2

These brakes are decent for the riders whom are just riding around on road or rails to trails and such. But any serious mountain biking...not so good. I had read reviews that they don't last long for some abusive mountain biking style of riding.