waterfall algae scrubber management question

[byronford]

Hello forum users,

I operate a 180 gallon reef tank with 80% invertebrates & am attempting to manage nitrate & phosphate levels with a waterfall algae scrubber. I feed 1/4 to 1/2 frozen cube daily (Mysis shrimp & Cyclops on alternate basis) & probably have more reef-dwellers in my tank than I should (pictures posted in 180 gallon thread). According to my API test kit, my phosphates have just reached 0.0 ppm but my nitrates are still around 15 ppm. The scrubber is still growing hair algae very rapidly (enough growth to block light from penetrating screen after only 7 days since I last cleaned it off) but will nitrate reduction now stop if there is no phosphate for the algae to use? Other than by feeding, should I be adding phosphate in order to tackle that last 15 ppm nitrate? I appreciate any input that you might come up with.

 

[saltyphish]

Your phosphates could be coming from the frozen cubes. I have read many people melt them and strain the water and rinse the food to prevent this. Also your nitrates are the byproducts of your bacteria doing what it should, breaking down the harmful ammonia and nitrite. I have also read the ati test kits for phosphate are not accurate or don't show a low reading. I don't see how adding phosphates will help the nitrates drop. The best way to drop nitrates is by water changes or by chemical filtration methods. How old is your scrubber, what size is it. The purpose of the scrubber is to grow algae that will eat the excess nutrients in your tank. If your scrubber has been running for a while than it may be undersized or something. You can also decrease how much you feed your tank. You could be overfeeding causing the uneaten food to add to your nitrate levels. Good Luck.

 

[tigerdragon]

What is your cuc like?

 

[byronford]

Sorry, not sure what a cuc is. My pH runs 8.0 to 8.2, alkalinity is 5.0 mEq/L, ammonia & nitrite are 0, Calcium is 400-440 ppm, phosphate is 0.0 (according to new Red Sea test kit) & nitrate is 10.0

 

[byronford]

I just purchased a Red Sea test kit & re-tested. Phosphate was confirmed as 0.0 ppm, Nitrate was 10.0 ppm. I had wondered about the accuracy of the API kits. Without doubt, the food which I put into the system is the phosphate source. I'm trying to balance what goes in with what comes out via sediment-trapping & algae scrubbing. Does 1/4 of a cube daily seem excessive for a fairly heavily populated 180 gallon system? The scrubber has been set up for about 2 months & the system is probably still coming to equilibrium after its addition. I'm attempting to achieve very low algae fertilizer concentrations without resorting to the vodka method. As far as the reason for my question goes, if the algae requires both nutrients to grow & phosphate is exhausted, will nitrate reduction cease for lack of phosphate?

 

[tigerdragon]

Cuc is clean up crew like snails, hermit crabs, sand sifters, urchins, etc. these help with algae, uneaten food, detritus very much a necessity. Just have to watch fish you run they may be coral safe and not invert safe. Also put shrimp and crabs in the cuc category.

 

[mcarroll]

I just purchased a Red Sea test kit & re-tested. Phosphate was confirmed as 0.0 ppm, Nitrate was 10.0 ppm. I had wondered about the accuracy of the API kits. Without doubt, the food which I put into the system is the phosphate source. I'm trying to balance what goes in with what comes out via sediment-trapping & algae scrubbing. Does 1/4 of a cube daily seem excessive for a fairly heavily populated 180 gallon system? The scrubber has been set up for about 2 months & the system is probably still coming to equilibrium after its addition. I'm attempting to achieve very low algae fertilizer concentrations without resorting to the vodka method. As far as the reason for my question goes, if the algae requires both nutrients to grow & phosphate is exhausted, will nitrate reduction cease for lack of phosphate?

As long as you have good flow and a normal compliment of live rock, denitrification in the live rock and sand bed should ultimately help with the nitrates. (This is what leaves "most people" with a phosphate issue but no nitrates.)

So, if your tank is in the condition of having any detritus in the sand bed, sump or rocks, deal with it harshly as it will always be a source of excessive nitrates. (Investigate all three areas to be positive!)

If not, just keep doing what you are doing - along with weekly water changes - and the numbers should even out. (I would probably not add clean up crew for this issue.) BTW, 10ppm isn't all that high. Unless you see that number increasing, I don't know if I'd do anything at all.

FWIW, "correct" quantity of food is determined solely by the size, quantity and type of critters you keep - not tank size. (Which is why so many people end up with nutrient issues.) Depending on all that, a quarter-cube of food per day sounds like a small quantity of food to me.

-Matt

 

[byronford]

In that case, my cuc is just 1 starfish which stays mostly on bottom & is frequently below sand. I tried snails but they disappeared (predation?)

 

[byronford]

Thanks very much for your comments. If I interpret them correctly then you think that, with good sediment clean-up, the algae scrubber should further reduce the nitrates regardless of presence or absence of phosphates? I've come up with a good method for de-sedimenting the substrate & rock pile. I can see that the sump is clean but the only area I cannot reach for cleaning is the substrate under the rock pile. I am proceeding under the assumption that nothing else can be done??? How common is the assumption that you need a deep substrate layer to encourage anaerobic reduction of nitrates? I don't like the idea of permitting anaerobic processes inside my system as I worry about what other reactions might be occurring down there (there seem to exist no means for testing for other products of anaerobic decomposition or methods of influencing what occurs in the deep sand bed).

 

[beaslbob]

Sorry, not sure what a cuc is. My pH runs 8.0 to 8.2, alkalinity is 5.0 mEq/L, ammonia & nitrite are 0, Calcium is 400-440 ppm, phosphate is 0.0 (according to new Red Sea test kit) & nitrate is 10.0

At a 16 to 1 ratio, 10ppm nitrates would have less then 1ppm phosphate. If your red sea test kit does not accurately read those levels you could be fine. I believe the salifert phosphate reads to .25 ppm or so.

So as your plant life (macros and other algae) expand and continue working, I think you will notice the nitrates dropping down.


my .02

 

[mcarroll]

+1 to what Bob said on both counts, and....

The thing with a deep sand bed that's crucial (at least one of the things) is that is shouldn't be disturbed...or very, very rarely. The reason is that you will (ideally) have all oxygen gradients within the bed so you have all the potential microfauna working for you....this does lead to sulphur production in some scenarios, but they should be unusual/rare and the only way they become a problem (or even known) is when the sand is disturbed. All of these processes are natural and critical to a well-functioning sediment bed. Your starfish - while obviously well-fed if you're not seeing him a lot - is murder on a good sand bed - way too big to coexist there in that small area....but I'm sure he keeps it pretty clean!! (Well-functioning sediment beds are NOT clean....not clogged either though.)

Read up on Jaubert/the Monaco Method if you want to try keeping a deep sand bed. I'd recommend keeping it in a separate-but-connected refugium to minimize disturbances and ease maintenance on it should the need arise.

That said, live rock should host a population of denitrifiers, but it may not be very big. Same for most non-disturbed sand beds. Going deep just allows a much larger space to develop for denitrifiers to live and a more complete ecosystem to form....it's not required.

-Matt

 

[Randy Holmes-Farley]

It certainly is possible for methods that require some balance to N and P get get limited by one or the other and then not be able to bring down that nutrient.

How long has the scrubber been exporting nutrients?

 

[byronford]

Thanks for your reply Matt,

The reason that I am trying to replace the de-nitrification function of a deep sand bed with that performed by an algae scrubber is that I have experienced set-backs which I attributed to 'other chemistry' in a deep sand bed. As a result, I have gone to a shallow bed & regularly de-sediment my substrate from top to bottom. To make this job easier I have developed an improved aquarium siphon (on which I am now patent-pending) which works much better on aragonite sand than the old one. Because those who advocate Jauberts' method will oppose any removal of sediment, I am interested to know how many of my fellow aquarists advocate this method. The answer to this question, of course has great significance to the potential marketability of my device. You point out that the sediment must not be disturbed in order to preserve the oxygen gradient. This advice is consistent with the method but I would like to know the answer to this question. If the denitrified water bathing the sand in the deep anoxic layer gradually returns to the aquarium circulation (thus lowering your nitrates) then why does this returning water not carry with it the toxic sulfur containing chemicals from this same layer? In the natural oceanic system, I believe that this is the reason for the physical separation of the reef from its associated mangrove swamp ecosystem which, according to predominant scientific opinion reduces nitrate produced on the fringe reef to molecular nitrogen. As reef-keepers, I think that the Jaubert method encourages us to try to replicate both fringe reef & mangrove swamp environment in too-close proximity, resulting in nutrient rich conditions which fail to favor the growth of our fringe reef denizens. I would like to know the thoughts of as many as possible on this subject.
Thanks, Byron Ford

 

[byronford]

Hi Randy,

I set the scrubber up in July. Have been practicing aggressive sediment control with each water change for years. I think you are right. My last nitrate was just below 5 ppm & I have a very heavy growth of hair algae that I plan to clean off later today (its been 3 weeks since last cleaning of screen. I'm taking this as proof that low nutrient levels are possible to achieve without deliberately setting up an anaerobic zone in your aquarium.