So I spent the weekend rebuilding my redesigned water cooling system. As some of you may remember I run an external system with the tank and pump sitting outside my house and the coolant is pumped into copper pipes through a vent in my computer room wall, and from there to the cooling loop in my computer. Anyway, the system, while performing brilliantly, had one major flaw; the tank was open to the elements. This of course meant that inevitably it would become overrun with algae in spite of being filled with a mixture of water and antifreeze. So a rebuild and redesign was in order. Now, I have a new and somewhat smaller tank. The previous tank held about 80l (roughly 20 gallons), whilst the new one holds about 50l (roughly 12 gallons) and it has a lid. I am using the same pump which I have spent portions of the summer rebuilding and servicing as well, so it should perform magnificently when I get the system up and running again. Yes, that's right, I'm not quite done setting it up yet. The pump is an Aqua Medic Oceanrunner 3500 - It's a 220V always-on model that pulls about 85W continuously, and as I want to become as energy-efficient as I am able to, without compromising on necessary performance, I needed an on/off switch. So I set about building a control panel consisting, at the moment, of a standard in-house lightswitch that will activate the pump. So, as the pump is now ready to go, and the hose have been hooked up to the pipes running into the computer room, I am now at the next intersection of this project. Mounting the blocks is no hassle, nor is filling or bleeding the system. I have the radiator hanging from the tank whilst protected from the elements as much as possible considering it still needs airflow. The radiator fans are powered by my computer by leads running through the same vent as the coolant pipes. I am currently building a control panel for the fans that will allow me to switch between 5, 7 and 12V. My concerns are that I have no realistic way of checking the waterflow and that I have no realistic way of checking the water level in the tank. I have found a floating tank level switch on eBay that I can use, though I originally wanted to build my own. But, a flow sensor that doesn't impede the flowrate too much I have yet to find, and trying to formulate ideas for building one has proved fruitless so far. I want a simple flowsensor that actives an LED (for instance) when it senses a liquid flowing through it. Does anyone know of anything like that? (Pics at a later time if you want them).