water change.. How long to wait.

Thanks for the advice everyone. You don't think my Bio load is too heavy do you???

As stated above, here is what I have in the tank. Remember it's a 120.

- In the tank I have the following: 4 inch sailfin tang, six line wrasse, two false perc clowns, orange spot goby, algae blenny, snails, hermits (not sure of the number) Maxima clam, 3 cleaner shrimp, 1-2 Emerald crabs.

- I also have a bunch of corals: some I forget the name of (that will be another post) others include Xenia, Colt Coral, Orange Sponge, Umbrella leather, Finger leather, green finger leather, frog spawn, Button pylops, star pylops, gonipora.

 

corals are not that much of a problem with regard bio load, unless you feed them to often with liquids, phyto, snow, etc IMO - there are tanks on this site where corals seem to fill every available inch of space ( not touching each other of course)

its the fish that put out the most waste and with your 120 , the fish you list at present, dont look like they are anywhere near over loading your system

rule of thumb (just a general guideline as all systems and capacity are differen） you could have 30 inches of fish in a 120 - I bet you not at 2/3rds of that with your present stock

20ppm nitrates is not an issue , if you dont have an algae problem

Uncle Jed offered a macro algae option , which you could look at to help you maintain, and then reduce your Nitrate levels (maintain as in not letting it creep up)

in addition - I have recently started using Purigen in my 70 and I am very pleased with the overall water clarity of my tank and my nitrates are between 0 - 10 ppm now ( a mid colour so Ill guess at 8ppm)

Steve

 

Filter socks should be changed daily. Not just daily when you have an issue but daily even when there aren't any issues. If you leave them for any period of time then all the detritus that they trap simply breaks down, rots and turns into nitrates. Same thing with wet/dry filters. They both provide an oxygen rich environment to turn it into nitrates but they lack the oxygen depleted/free zones to convert nitrates back to nitrogen gas. Just make sure you keep them clean or they cause more problems than they solve.
I don't agree with the notion that a healthy tank would have a nitrate reading. If the tank has enough of the proper bio-filtration and the environment they need, the nitrates will get converted back to nitrogen gas and you won't have a nitrate reading. If you have a nitrate reading, then something is out of whack somewhere in the system and if its out of whack it can't be healthy. Whether it's not enough Live Rock, if you have a nitrate factory somewhere (dirty socks, bio-balls, etc..) or simply dead spots (water flow issues) where detritus is allowed to settle.

Clams and Xenia in your sump and/or display will do more for your nitrates and phosphates than algae will.