purity (quality) of saltwater

can someone please explain how to measure the purity or water quality of our reef aquariums? also how can i make the de-nitrification process keep up with the nitrification process? i currently have a refugium with a footprint of 12 by 18 inches with 5 inches of sand with very low flow. my display tank is a 29 gallon with a 10 gallon sump. how many square feet of deep sand bed should i have to keep up with the tank's nitrification process? i have about 40 lbs of lr, i run coral life 65 protein skimmer 24/7, i use a filter sock that i change out regularly and i don't overfeed. i was doing 10-20 gallon wc's weekly and got nitrates down to 40ppm from 180ppm. was staying at 40ppm as long as i did the wc's. here lately i haven't been able to buy any salt so i haven't done a wc in 3 weeks, now my nitrates are back up to 160 -180ppm. awhile back i experimented and disconnect the refugium and let it run by itself with a 10gallon sump. in 2 months the nitrates went from 180ppm to 0ppm and i lost all the macro algae that was in there. so, i know the deepsand bed works but alot slower than the tanks nitrification process. i thought about adding a couple more deep sand bed containers. what do you think?
my water params are
salinity 1.026
ph 8.3
ammonia 0
nitrite 0
nitrates 160ppm
phosphates 0
cal 440ppm
alk 11dkh
mag 1400ppm
i want to have a self sufficiant tank so i can get away from all those wc's.
i dose essential-elements and coral-vite once a week, sometimes once every 2 weeks (depends on wc's)
i also have a problem with ammonia in my top off water, its 0 coming out of my rodi filter but when i store it in my brute trash can it developes ammonia for some reason. if i hook up a auto top off coming straight out of the rodi filter that might help eliminate the build up of nitrates. what do you think about that? sorry about the long read but i just don't understand how some people can have 0 nitrates and others cannot even get low nitrates. :;D please enlighten me!!! lol ;D;D;D

 

Just a few things I noticed:
Could use a better skimmer. Coralifes are at about the bottom of the range IMHO. What is your stocking situation? What and how are you feeding? Amount of rock? Did you wait for a full and proper cycle or just to read 0 ammonia and 0 nitrites?
Also the addition of ammonia from the bin will always create nitrates. The cheap rubber from the brutes can leach chemicals/pollutants into the water during storage. Getting a good FDA approved food-grade container will help out quite a bit.

 

i have 1 small chromis, 1 scarlet hermit, 2 turbo snails, alot of stomatella snails, alot of pods, bristle worms and feather dusters. tank has been running about 5 years now, i am pretty sure its cycled.
corals are candy canes, kenya, xenia, gsp, hairy shrooms, zoas and toadstool. i feed phyto and microvert lightly once a week. chromis feeds on whatever he can find. i have about 40lbs. of lr

 

I've heard a lot that cheap trash cans can leach bad things. Never heard the Brute trash cans are bad though.. I know Randy Holmes Farley (the guy that writes all those reefkeeping articles) uses 3 44 gallon Brute trash cans. I suspect that is not really your problem.
You said you lost a lot of macro... how much is in there now and what kind of light do you have on it? With all the nutrients in there and a proper light the macro should grow. If it got thinned out I would get some more from a fellow reefer.

I don't have a refugium and wasn't to keen on replacing my sump with a new big refugium/sump so I built an algae scrubber. I went from super high NO3 to NO3=0 in three months. It requires a lot of research though and must be maintained properly where as a refugium is much easier and simple.
I tried nitrate coil-didn't work... too finicky
Kent marine nitrate sponge- never got anywhere with this.. I think you need a lot so it gets too expensive.
Bought some Purigen but never used it(still in my fish cabinet) since the Algae scrubber started working well. I've heard good thing about it.
Since your'e kinda in emergency territory you may want to give the AZNO3 a try.

 

yeah i lost alot of my macro when i disconnected my dsb refugium from my system and let it circulate by itself (experiment). it was a success. nitrates went from 180 to 0 in about 2 months. macro died because of no nutrients.
i have some now but nowhere near as much as i used to have. i did try the denitrator coil also but was not working fast enough either. i believe i will try to add as many dsb containers as i can. run them in series with each other coming from the sump after the filter sock so as to not let anything get in them that would cause a build up of deitris. the algae scrubber seems too complicated for me but i am glad that its working for you.