I have an article for you to consider. Here it is, from my site:
Nitrates: They Can Be Beaten Down Into Submission.
Nitrates are a part of nature in the ocean, and correspondingly in our tanks. As waste breaks down in your aquarium, it cycles from ammonia to nitrite to nitrates. The first two are highly toxic to marine life, and we make it a point to make sure our tanks test zero for these. However, nitrates aren’t as bad, and sometimes are even a little beneficial.
Specifically, few organisms need nitrates. Both micro and macro algae love the stuff, while fish tolerate it. Invertebrates suffer if the levels are too high, but a little is required to keep clams happy. In our goal to match NSW as closely as possible, we strive to keep nitrates down to a minimum at 10 ppm or less.
First things first -- what is causing the nitrates in your tank? Bioballs, biowheels, filter pads, foam blocks & tubes, and under gravel filters all contribute to the production of nitrates. Overfeeding is another cause, and a lack of water changes will be another factor.
Nitrates are in the water column, not your substrate or rockwork. Frequent large water changes will quickly reduce the amounts of nitrates present in your system. I battled with nitrates for years, even when using Nitrate Sponge on a weekly basis. I’d change 5 gallons in my 29 gallon tank and see the nitrates drop from 80 to 60ppm, only to rise again. I’d cringe when I’d run a new test and see the fluid bright red before the timer was even set!
Once I removed the 3 year old under gravel filter & my Penguin Biowheel filter filled with bioballs, I was finally on track. I did three 10 gallon water changes in one week, or 33% at a time. Nitrates were down to 20ppm. I became more meticulous with my water changes, changing 7 - 10 gallons each time every two weeks.
Later on that year, I added a sump & refugium to that tank. The saying “Dilution is the Solution to Pollution†proved to be absolutely true. The macro algae in the refugium as well as the small sandbed helped denitrify my tank, and nitrates are ranging from 0 - 2ppm with a water change only being done every other month.
Last November I bought an existing 55 gallon tank filled with 7 fish, 120 lbs of live rock and crushed coral substrate. The previous owners never tested their water, and the nitrates were 200ppm or more. Through a series of major water changes in those first two weeks, nitrates were lowered without stressing the fish. The substrate was replaced with a DSB, and the canister filters with biowheels were removed as a sump was incorporated. Nitrates are down to 7ppm after three months, and only one fish was lost during that period (probably due to starvation… it never looked healthy).
If your tank is suffering from high nitrate levels, the success of your reef will depend on your being able to get this under control. Changing 100% of the water would be the ideal, but it may shock your corals, fish and invertebrates in the process. A more gradual way is recommended.
55 gal Reef Example: Make up 20 gals of fresh saltwater in a trashcan in front of your tank. Drain 10 gals of tank water into the 20 gals of new water, and let that mix. Pump 10 gals of that water back into your tank, and let the power heads mix that water up in your tank for a minute or so. Then repeat this three more times. Dispose of the now polluted 20 gals of water. Make up another 20 gals of fresh saltwater, and repeat this procedure. As long as your temperature and salinity match the tank, your inhabitants won’t be affected adversely, and with each rotation of water, the nitrates are being diluted and removed from your tank.
Simply pulling out all of the water in one massive water change puts stress on your entire tank. Doing small water changes consistently won’t bring nitrate levels down. At best, it will maintain them at their current levels. Using the example above, a tank that was at 80ppm would be around 30ppm after a couple of hours work and your population will be happy and unaffected. Once your nitrate levels drop, they are easily kept low with regular water changes, as well as the use of a DSB and macro algae.
Your tank will be healthier, your reef happier and the nitrate problem fixed!
------------------------
Huge water changes back to back will solve this, and once they are low they will stay low. When you test* your nitrate, are you holding the beaker at an angle with the card behind it? If so, be sure you look at the matching color, then divide by 10.
You may need to seed your sand bed with two more cups of livesand from someone in your area.
If you modify the skimmer's impellar with mesh material, it'll work much better. I know because I tried it out myself.
*Salifert kit
There is no reason to give up. It isn't that bad a reading.
