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Q&A Lowering Nitrates


What is the lifespan of dry live reef rock once it’s matured in a reef tank?

If you do it correctly, your dry live rock can last forever.  The real issue is when it becomes like a sponge.  When it absorbs things like phosphates and nitrates.  Then over time the dry live rock can become so full with all these nutrients that it can start leeching it back out into the water column.  And then you’re going to see spikes of things like nitrates and phosphates. And you might have huge algae blooms and other problems.  So as long as you take care of your reef tank, the live rock can last forever.

We have a water softener. How does that impact the need or the cleaning of an RO/DI Filter. Should I use the softened water to make RO/DI water, or should I use the outside spigot that does not go through the water softener?

That’s a really excellent question, and I have no expertise when it comes water softeners.  But what I would personally do would be to measure the TDS of both the spigot water and the water softener water, and use whichever one is less.

Here in the Coachella Valley we have hard water, meaning higher total dissolved solids.  Our TDS is around 150.  When I used to live in Seattle our TDS was around 40, so much softer. 

At the end of the day, you’re going to adjust your RO/DI filter to suit your aquarium needs. If you live in an area with a lot of chlorine and chloramines, you might want to buy a specific DI resin that will remove those chloramines. You also might want to add an extra carbon filter because activated carbon does absorb chlorines.

I’ve read that RO/DI units love high water pressure for higher efficiency. Is that right? And why?

RO/DI filters run much more efficiently with higher water pressure and that’s because of the back pressure you need created for your RO membrane to function.  You don’t need high pressure for your carbon, sediment, or DI resin canisters, water just passes through there. Sure, a higher water pressure is going to be able to push through at a faster rate, but where you really need it is for your RO membrane. 

Reverse osmosis needs water pressure.  You can watch this video clip to understand what exactly reverse osmosis is.

Osmosis is when water molecules travel through a semipermeable membrane from an area of lower solute to an area of higher solute. For example, if you have pure water on one side and salt on another side, the water is going to move toward the salt for various reasons.

But with reverse osmosis you are reversing that.  You are taking the area with the salt and applying pressure.  And when you put pressure into that water, it forces the smaller particles, which are the H20 through that membrane. So yes, good water pressure is important.

I’ve got a 60 gallon fish only tank, pH is 8.2, temp-80, alk 8.0, ammonia 0, nitrite 0, nitrate 60+, salinity 1.026. I have live rock, little algae and the water is crystal clear. I do regular water changes with RO water. I have 2 jets to circulate and one is pointed up to ripple the water surface. For the life of me I cannot get the nitrate down, any thoughts?

Two thoughts.  60 nitrates is high.  My nitrate test kit only goes up to 50.  But I have had this exact same struggle.  I spent months trying to lower my nitrates.  And there are two ways to lower your nitrates. 

The first is with biological filtration.  There are aerobic and anaerobic bacteria.  I’m no scientist here. My understanding is that aerobic bacteria will convert the ammonia to nitrite, and the nitrite to nitrate.  But you need anaerobic bacteria to convert the nitrate to nitrogen gas. 

Well, where do you find that anaerobic bacteria?  It is found deep inside live rock or deep in a sandbed.  If you don’t have very dense live rock or a deep sand bed, you might not have a lot of that anaerobic bacteria. 

So what can you do? First you can add some more live rock, but that is going to take time to populate with anaerobic bacteria.  You can always buy things like Brightwell Xport Biobricks, Marine Pure also sells biological media.  The mistake I made with ceramic media, is I put them in high flow area, thinking that high flow through the media would be best.  But if you are trying to lower your nitrates, my understanding is that you want it in a low flow area where the oxygen wouldn’t circulate through it.

But if you are at 60 nitrate, you might really struggle getting it down.  So what can you do?  A huge water change.  Honestly, that’s what I had to do on my 120 gallon tank.  I was above 50 nitrate, and a 50% water change brought that down to around 30.  If you remove 50% of the water, you are going to remove 50% of the nitrate.  That by itself might be enough, because maybe your beneficial anaerobic bacteria will be able to keep up and keep the nitrate at 30, but maybe not.  So you will want to increase your biological filtration.  If you can’t add more live rock, then pick up some ceramic meda and put it in a sump, in a rear filtration chamber, or even a HOB filter.