Nitrates...

[Water and Salt]

I know you have heard it a million times, but I have a nitrate problem. My tank specs are as follows:

90gl display
40gl sump
200lbs live rock
live sand bed
Coralife 225 skimmer

Lawnmower blenny
Scooter blenny
Watchman Goby
Pair of maroon clownfish
Anemone
Zebra eel 20+ inches
2 cleaner shrimp
a few soft corals
clean up crew

ammonia: 0
nitrites: 0
Phosphates: 0-.25ppm
Nitrates: 30ppm

The tank has been set up for about 6 months with rock that has been in an established aquarium for 2 years. I seem to have no common causes for major nitrate build up (wet dry, dead spots etc).

Here's my guess, tell me if I'm wrong...

The eel eats well over 2x as much as the rest of the inhabitants combined. Since there are no obvious reasons for high nitrates, I blame it on him. All of the organic matter introduced into the tank will, one way or another, be converted to nitrates. The ammonia and nitrite are 0, so the biological processes are not being overwhelmed, but effectively converting all waste to nitrate.

Sound theory, or rantings of an idiot?

[leebca]

All your nitrates produced in the aquarium are coming from the marine life forms that are utilizing nitrogen foods. This of course includes the eel but don't forget the other life forms (of which there are many, which is another point).

The tank is a mix of invertebrates and fishes. To be honest, the tank should either be a FOWLR tank OR a reef tank. Too many fish in there to properly try and control the nitrates so that the corals are happy. An easy and properly functioning reef tank should have very few (if any) marine fishes.

You would have to work hard (many large water changes and frequently) and/or pay out a lot of money (nitrate and ammonia removers, reactors, deep sand bed, refugium, etc.) to try and control such a bioload of nitrate producers. Your setup seems to me to already be (normally or standard wise) maxed out to handle the 'normal' nitrate load (e.g., LR quantity is very good). [Although I don't know if that is the optimum skimmer or not.]

[CharlotteSteve]

I would try macro-algae first. Some type of calurpa, but steer clear of the bubble.

[Water and Salt]

That was my thinking. when I was setting up the tank I was planning on making it a FOWLR, but I came across a great deal on the rock, it already had corals attached, so it is now a FOWLRAAFCAT (Fish Only With Live Rock And A Few Corals And Things)
Most of the corals seem to be doing fine so far, but I know they won't be fine for long if the nitrates remain that high.
You mentioned that the skimmer might not be good enough. Any recommendations? could I double up and put in 2 skimmers, or would that really accomplish anything?
My sump already has large amounts of macro algae. about 3 football size balls of chaeto, a bunch of red caluerpa(?) and some other stuff that came with the rock. should I get more? different types?
how deep does a deep sand bed need to be to start culturing anaerobic bacteria?
I just put in a bag of 'Pura Nitralock'. Nitrates immediately went down to around 10ppm, so I ordered 2 more bags.
I appreciate the input... Any other suggestions?

[leebca]

Well, you're even doing more than I anticipated. Most of the options are already in effect.

Make sure the Chaeto has enough lighting. (It doesn't take much). Chaeto, for its surface area and volume is usually the best for handling nitrates. Get as much as the sump area will hold and still not hold back or block circulation. Remove the other if Chaeto will grow in its place.

Skimmers are good at removing organics. This would be (hopefully) before they are taken up by bacteria and move along the nitrogen cycle to nitrates. For the right skimmer function, the issue is flow rate. Won't go into that here, since it was covered in this post: What is Water Quality. Read that link regarding especially skimmers to make sure you've gotten the right one, then keep it properly cleaned out (daily or no more than every other day).

Sand beds that operate a denitrification beds need to be about 4 to 6 inches deep depending upon the particle size. It runs about 1/2 the area in most cases, but in yours I would put one in for the full bottom area. This will reduce water volume and even more reduce the kinds and numbers of nitrogen 'eating' marine life forms you can keep.

My best of all suggestion would be to choose -- fish or reef.

Chemical absorbents do help. That's the expensive part of your efforts.

[Water and Salt]

Thanks for the advice

Right now, I have 3" or so of fine sand, I guess I'll add some more, get it up to about 4".
I can retool the sump to fit a lot more chaeto, so I'll do that to.
I'll start looking for a better suited skimmer as well, but to be honest I cant afford a brand new $500 skimmer at the moment, so I will see what I can find.

I foresee many water changes in my near future, hopefully fewer if I can get the system running more efficiently, but either way there will be many.

As for choosing 'fish or reef', I'm not giving up the fishies, and the corals that are there are firmly in place, so the only thing I can do right now is do my best with the nitrates and see if it will continue to work.

Again, thank you for the help, I'll see what I can do!