we need to know what gpd your ro unit is 2 gallon in 7 hours does sound slow. the flow restricter is needed for the unit to run correctly, water will flow freely from the waste and drip from the product pipe, you should get 3 times more waste than product im affraid they are horribly inefficient, i have a 100gpd and takes me an hour to get a gallon of ro water at 40 psi.
kole tangs are normally peaceful as for adding a clown you need to add one much smaller than the one you have that way they wont fight to death as the larger one will become the female with just a few small scuffles lol
well i have a similar system and have 2 regals a blonde naso and a kole tang who all get on great although il be rehoming one of the regals soon, id leave the boxfish mate youve to much rockwork to shift if it dies as they can release toxins when they die, tought about a wrasse? i can recommend to silver belly bannana wrasse peacefull and out a fair bit with no special requirements
i have a massive flatworm ploblem i hate them! i also have a manderin he desnt eat flatworm! so i now have a silver belly bannana wrass who eats baby flatworm but not ennough to really notice the diffrence. watch the 6 line as they can be aggressive and be prepaired to think you've lost him as quick as a flash they bury themselves in the sand lol takes a while for them to settle in! really pleased with the wrasse tho great fish! its still possible to get flatworm exit but it kills all podlife in your tank not just the flatworm which is why ive not used it, wouldnt have been a problem untill i introduced the manderin so catch 22 really
to be honest i'd stick with t5's i started with halides but i recently built my own t5 set up because of the heat factor and running costs i keep softies lps and sps and havent noticed a diffrence since i changed