What exactly were the test readings? That will help the chemistry buffs help you out. Also be sure you top off the tank DAILY. Salinity swings quickly in nanos. I usually top mine off every afternoon at feeding time.
KH is the measure of the buffer in your tank. The buffer stabalizes you ph. Organics come from food and fish waste. If your nitrates are high you could be feeding too much, have too much live stock, not enough filtration, or a combination of any of these.
To increase flow just get yourself a small powerhead to stick in there. You could position it so that the current of one power head crosses the current of the other, or have one shooting from back to front and one shooting from side to side also. Just make sure there arent too many dead spots, where the water doesnt circulate alot.