Which RO machine for angelfish breeding tank?

[Kelly5978]

Not sure if I've put this in the right place, but I want to purchase an RO machine for better water in my angelfish tank. I'm told some systems are better than others. I'm in an apartment, so I want the smallest one. I'm also poor, but don't want to go too cheap and get junk. What brand of RO machine is best? Also, what are the best products to add minerals/electrolytes back in a breeding situation? I'm aiming for a kh of 4, gh of 3-5 and ph of 6.5. Seachem advised me to use acid/alkaline buffers for kh, and replenish for gh. Any advise on amounts? Brands? Any help at all is appreciated. I've been having trouble keeping fry alive. I've been trying to breed 3 pair of angelfish for months, and feel like a failure ?. Thanks