Out Of Control Nitrates!


Hey, everyone!

About out tank: We've had a 90 gallon reef tank since September. We have someone who services the tank, but we also get lots of advice from the LFS's in the area. Our filtration is a protein skimmer with a refugium (with a little caulerpa algae in it) and we have sand and rubble rock as substrate. We keep live rock and soft corals along with our fish and inverts: currently 2 clownfish, a regal blue tang, a yellow tang, a sailfin tang, a fairy wrasse, an orchid dottyfish, a pygmy angel, 2 pj cardinals, a scooter blenny, a yellow watchman goby, a pistol shrimp, a sand sifting starfish, 2 peppermint shrimp, 2 anemones, and a handful of (cone?) snails.

Problem: We've had a series of episodes of nitrate spikes--big ones!--that have resulted in us losing a good number of our stock; this time we lost our valentinI puffer and six-line wrasse. We've been doing partial water changes like crazy; we're doing another one today, but in the past month we've done at least 4 10-15 gallon water changes. When we test water, everything else is normal, and we've taken water to the LFS to verify what we're finding: nitrates spiking 80-100 ppm. We've tried changing the feeding schedule and reducing the amount we're feeding, but that doesn't seem to be effective either; we feed six days a week, alternating one day seaweed and one day a mixture of frozen cube food with Garlic Elixir.

Has anyone else had a similar problem? Is there something we need to do that we're not doing? It seems like all the fish people we talk to are at a loss, and can really think of nothing other than overfeeding that could be causing this. Someone suggested using an EcoBio Block, and I've also seen a product called De-Nitrate. Does anyone have experience with these products?

Would love to hear any advice or suggestions you might have!



Your water changes actually seem pretty small to me but I am pretty inexperienced with SW. I am only just starting a 20 gallon nano tank without a sump or refugium so I can't say much about your situation. Also, I'm sure the person you've hired to help is doing water changes as well.

It seems like the Saltwater threads are not always as busy as the FW. I wish I could help! Hope one of these more experienced Saltwater keepers can answer your questions...

Good luck!


I only have a small tank lol, but for starters a few pictures would help of the set up ref, any kit and chems is there any cyano problems? Whats the flow like? How much live rock is there, a skimmer is not really biological filtration and what water are you using ? Its strange you only have a nitrate issue.


HI Dorothy,

A few questions for you.
1) Have you been doing the water changes yourself or letting the service person change it for you? Whoever is doing it, are you also doing a sand vacuum as well?
2) Also - is your total water volume 90 gallons? or is it 90 gallons + 40 gallon sump or something?
3) Could something have died in your tank and you don't know it?
4) How has your macro algae been growing? Any growth to it? Do you have a light on the macro algae?
5) Have you been running your protein skimmer? How long? And is it skimming anything?
6) Do you have any filter sock or sponges that you are using in your refugium?
7) When you say you've done water tests and everything else is normal. Can you provide us the numbers?

Here is my perspective on your current situation.
It's a given that you have a decent size bio-load. I am wondering, whoever is doing the water changes, are they doing a sand vacuum for you as well? Because, water changes just by itself is actually the least efficient way in exporting nutrients. If you don't get the detritus out of your tank, it will continue to build up and pollute the water column. Also, 4 x 10-15 gallon of water changes in the past month is very little for a tank your size. You need to do at least 25% water changes along with sand vacuum to address your issue, so that's about 23 gallon of water for each water change. I am also thinking if you have sufficient flow in your tank to ensure detritus does not just settle in a spot and build up.
I personally would not dose or add any sort of eco-block to your tank.

Let's see where you are at with my questions above and we might be able to help you.


I have a mature 7 year old Saltwater tank with a deep sand bed, about 3". About 4 years ago I had the same issue and lost much of the livestock. I had started cleaning the sand with a vacuum and turns out that it was bringing up the bio waste from the sand bed. I stopped vacuuming and let the tank re-cycle. Have not had any problem since. Don't know if you are disturbing yours or not but it might be worth taking a look.


Deep sand beds are typically 6"-8".

"Using a deep sand bed with fine grain sand is great because of the increased biological filtration. It will promote both aerobic and anaerobic bacteria helping to break down waste and remove nitrates. A deep sand bed is typically 6″ to 8″ deep. Within the first 2″ to 3″, aerobic bacteria will thrive and help breakdown waste and produce nitrates. As you go deeper into the sand bad, the water will be less oxygenated and therefore anaerobic bacteria will thrive. This type of bacteria is very efficient at denitrification which will turn nitrate into nitrogen gas."

Marine/Reef Aquarium Sand: Deep Sand Bed or Shallow? Coarse or Fine Grain Sand? Find Out! - Marine Depot Blog

Anything less than that you need to clean, stir, and vacuum very often so detritus does not have a chance to settle. Leaving your > 6" sand bed alone creates what they call an old tank syndrome. This is a pocket of detritus build up, when disturbed will release the toxins and possibly harm all tank inhabitants and can be very dangerous.

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