Ah! The only thing I do not know:
How good zalman's liquid is.
Now, they are a very smart company so I couldnt tell you.
However, I can tell you that it is highly doubtful that any person has more pure water than me who has kept running this long with pure silence in the pump. I can say that I put less than a half bottle into the tank. Apparently, the reserator needs very little help keeping the oxidation out. Zalman has annodized almuminum, and makes things perfect. My success could be due to the fact that we are using the best equipment. I do remember how for the first year Zalman suggest just distilled water no additives. So, it was designed with non corrosive additives in mind, something no other was or is. They changed this as it was a bad idea for many, and some it was a great idea. So, probably 4-5 ounces of WW would be fine. I assume you have more water in your setup, half a bottle each fill I would use. It's cheap too and easy, no ordering, just an autoparts store and a grocery store for steam distilled water.
God might be on my side, so supernatural things could be the reason. never really know. it might be a tad miraculous. I mean it is an eheim 300 lasting in a hot environment silent for years working.
NOW: for your 2nd tower design... wow. you are my idol. I didnt know that would even work. You could do dual high end gpus with that setup easily. That is a LOT of water and radiation surface area.
Makes me know what I am goign to buy this year...
yup! another tower