Hi. The first thing I would suggest is double checking your reading with a secondary source such as an LFS to verify if the nitrates are indeed at 180 ppm (extremely high even for FOWLR). You should also see tons of unwanted algae growth all over your tank if the nitrate levels are anywhere near 180 ppm.
If nitrates are sustained at this level, your fish may develop problems such as Head & Lateral Line Erosion from poor water quality. High nitrates levels like this are a direct result of organic material (mainly uneaten food and fish waste) decomposing, going through the nitrification cycle, eventually ending up as nitrates and not being exported properly. It is very possible that your water will test high for phosphates as well.
With that said, I want to make you aware of a few things before you consider a denitrator which will definitely remove nitrates from your system when set up properly. That reefkeeping.com article is a great resource.
Here are some simple solutions which can generally produce low nutrient (nitrate and phos) levels in any system when properly utilized:
- Use the largest and most effective protein skimmer. A skimmer will remove organic material before it has a chance to break down into ammonia, eventually nitrates and this is your single biggest defense against high nutrients in a large FOWLR system with a high bio load. Again, a strong skimmer is invaluable in a FOWLR setup such as yours.
- Use macro algae such as chaetomorpha to naturally export nutrients in a refugium or sump. More chaeto (larger fug area) and plenty of daylight (5-6K CFL), can be utilized to export larger amounts of nutrients.
- Use ONLY RO/DI water for your top-off and freshly mixed salt water. Tap water adds unknown amounts of nutrients directly into your tank. Although nitrates are regulated under 10 ppm by the EPA, there is currently no maximum contaminant level on phosphates and therefore tap water can have relatively high phosphates for a salt water tank.
- Use a Deep Sand Bed (DSB). This is more of a long-term method and won't yield any immediate results.
A note about why water changes merely buy you a little bit of time:
As a conservative rule, nitrate levels in a fish only tank should not exceed 30 ppm. Although fish will appear to survive at higher levels, you are risking their long term well being. In your 130 gallon tank, it will take a single 90% (117 gal) water change to bring the nitrate level down to an acceptable 20 ppm. It will take even more water to accomplish the same result as multiple smaller water changes. For example if you opt to do 25%(32.5 gal) water changes, it will take a total of 9 water changes and 292.5 gals of total freshly made salt water to reach a nitrate level less than 20 ppm. Water changes of this magnitude are not only ill advised, it's simply not feasible. As you can see, water changes put you back at square one and with your high bio load, it won't be long before the nitrate levels are back up again.
You need to tackle the root cause to eliminate the problem. High nitrate levels in your FOWLR is a result of a large amounts of organic material breaking down. Ramping up protein skimming on this system can drastically reduce the amount of organic material in the water column, limiting the amount of nitrates produced. If you are skimming at capacity with one skimmer, it is severely undersized.
Now, all I know about your setup is that it is 130 gals and you've attempted water changes. Please provide more details about your existing filtration for a more specific solution. Do you use a skimmer, refugium, sump, canister filter? Also how many fish, fish size, and feeding habits?
