Experiment: Trace Element Limitation in Reef Tank?

[taricha]

Is growth in (some) reef tanks governed by trace element limitation (sometimes)?
Maybe? Probably?
The argument goes like this. If all macro nutrients are provided in abundance without care taken to replace the undetectable trace elements, then eventually some crucial scarce resource will be depleted to the point that growth slows. I should probably call these "micro-nutrients" instead of trace elements, because the limiting factor may not be an element per se, but perhaps some vitamin etc that is scarce and crucial.
Straightforward, but showing that this actually happens is a different thing.
I am keeping my tank replete in the macro nutrients: N, P, (in my case Si), Ca, Alk, Mg, and making sure my inputs of these nutrients stays absolutely consistent. Then measure anything informative I can measure to track growth in my system. In theory, if a micronutrient becomes limiting then the consumption of the macro nutrients should slow or stop, and their levels should rise with the same inputs.
Questions:

• Can growth be shown to slow dramatically in a tank with all major nutrients provided in abundance due to a depletion of micro nutrients?
• Can the limiting micro nutrient(s) be identified?
• Can the organism(s) being limited be identified?

So I started by measuring everything on day 1 and dosing all the micronutrients I could think of. After 2 weeks - here's data so far and a few comments.

Line is a 2-day average of readings. NO3 I divided by 100 so it could all be on the graph. Not all 3 are precisely comparable. NO3 has huge error bars compared to the others, It's not necessarily steady at 10 - I just can't tell between 10 or 7 or 15ppm. Also it wasn't really moving opposite the other two the first few days, I just dosed more NO3 first few days to get it up to 10.
Si may look like consumption is slowing but it's not. Here's another graph showing same nutrients with the daily addition/consumption...

I'm upping Si dose 10% a day until I get to 1 ppm Si. I find it weird that Si consumption is increasing almost exactly at the same rate as the dose increase and drops back to near the exact same level every day. I'll redo this graph when I figure out how to calculate and show the food inputs of my 2 cubes a day to P & N.
One last graph - Ca, Alk, and pH. I had to scale the Ca weirdly to fit on the graph.

Final comment on the data for now - Most everything moved as expected for days 1-5. After adding a bunch of trace elements, the consumption generally increased. At first I thought the leveling out and the rise from day 6 to 9 was the onset of the limitation, but a likelier explanation is that days 7,8 & 9 we had cold cloudy weather, and my tank gets a few hours of natural morning sunlight from a window. Sun comes back out day 10 and following and growth pics back up.

 

[taricha]

Oh, what's in my 70 gallon system eating all these nutrients?
Coral: some SPS, majority softies, zoas,mushrooms, photosynthetic gorgs, a big plating photosynthetic sponge (with a cyano symbiont), macroalgae - chaeto and caulerpa some in the display and a ton in the sump. Diatoms, Coraline algae, Lots of sponges in the dark underside of lots of rocks. Also a cyptic 5gal bucket that I suspect will colonize with sponges soon.

 

[Dennis Cartier]

Double Post

 

[Dennis Cartier]

I commend you on your desire to look for these subtle relationships. I agree that there are almost certainly limiting elements at any one time in each tank. Figuring out what is the limiting element is, and providing it in sufficient quantities to ease it's limitation, without driving it too high is the challenge.

Dennis

 

[Mortie31]

How do you intend to identify what may be missing, as even ICP testing has limitations at very low levels with lots of elements?

 

[Mortie31]

Having reread your thread, isn’t this what the Triton and DSR methods do anyway? You may be looking to go one step further to ascertain if deficiency in a given micro element is detrimental or not if that’s the case good luck.

 

[taricha]

How do you intend to identify what may be missing, as even ICP testing has limitations at very low levels with lots of elements?

...isn’t this what the Triton and DSR methods do anyway? You may be looking to go one step further to ascertain if deficiency in a given micro element is detrimental or not if that’s the case good luck.

Yep. Notice I'm not attempting to measure the micro-elements. I'm measuring the rate of macro-element consumption and concluding a limitation from that.
And once the data is pretty convincing - then I'll add select micro-nutrients back, and see which ones boost growth the most and which don't.
This should work around the issue that ICP would have of say Fe being undetectably low whether its limiting or not, and same for complex nutrients like B Vitamins which most all photosynthesizers have an absolute need for, but is undetectable in the hobby as far as I know.

 

[Flexin]

This is interesting. I was struggling with how do you know when to start adding trace elements to a tank. But this will help with the second part of the question which is will it make a difference.

 

[taricha]

Things I'm measuring, test kit, general level in this tank, and comments:
NO3 - Red Sea - 10ppm - not precise enough to tell me anything for this test. I need to upgrade.
PO4 - Hanna Hi736 (convert from P) - 0.100ppm - great test
Si - Hanna HI705 (convert from SiO2) -moving from 0.10 to 1.0ppm - great test
K - Salifert - tests 420-460ppm Not shown on graphs because it tracks with other nutrients - good test
Ca - Red Sea - tests around 380-450ppm - good test
Alk - Red Sea - tests around 7.5-8.5dkh - okay test +-.2 almost obscures actual variation
Mag - Salifert - tests around 1300-1500. Not shown on graphs because it's tracking with Ca/Alk - good test
pH/Temp - Hanna Hi98108 - tests around 7.8-8.2 - great meter (2point temp adjusted calibration) once I learned about borax and cream of tartar reference solutions it's even better
I - Salifert - can't get a reading of even a known concentration - unacceptable test.
Fe - Hanna Hi746 - levels in tank never high enough to be accurately read.

Anything else I should be measuring or should watch for more closely?

 

[taricha]

This is interesting. I was struggling with how do you know when to start adding trace elements to a tank. But this will help with the second part of the question which is will it make a difference.

I'm trying to post the data for others to see, because yes - there's some interpretation involved. Hopefully it'll reach a point where it's absolutely clear what's happening. In addition to watching the numbers, I'm also watching the tank itself - algae growth etc.
When everything is telling the same story for several days, then I'll think we have something.
maybe it'll work.

 

[Randy Holmes-Farley]

If the alkalinity and pH are not held steady, variations in them may confound the interpretation.

 

[Flexin]

Randy, what is your take on using trace elements and when should they be considered or not?

 

[Randy Holmes-Farley]

Randy, what is your take on using trace elements and when should they be considered or not?

I think it depends on your other husbandry techniques, but in my system, even with 1% daily water changes and good feedings, some were depleted.

I think trace element dosing (and removal) is the next big frontier in reef chemistry. What to add and how much, and what might already be in excess, is somewhat complicated to know and will vary tank to tank.

Here', for example, are some results I found for my system:

My Triton Testing Results: By Randy Holmes-Farley
http://www.reefedition.com/my-triton-testing-results-by-randy-holmes-farley/

Molybdenum (Mo). Molybdenum is low, and if that is true, it’s an interesting and potentially important result. I don’t typically add any trace elements. I may consider adding some molybdenum as it is biologically important.

Vanadium (V). Triton can just barely detect the natural level of vanadium (1.8 µg/L) since their LOD is 0.9 µg/L. Still, detecting none suggests it may be depleted, and is another possibility for dosing.

Zinc (Zn). The zinc is about spot on, so there’s not much to say about it.

Manganese (Mn). Triton can just barely detect the natural level of manganese (0.17 µg/L) since their LOD is 0.12 µg/L. Detecting none suggests it may be depleted, and is another possibility for dosing, but I have less confidence that this one is really seriously depleted since it is so close to the LOD. But Mn is biologically important and I will consider it.

 

[taricha]

If the alkalinity and pH are not held steady, variations in them may confound the interpretation.

I'm new to measuring pH, I need to re read to get a better grip on what ph changes signify in connection with other nutrients, and under what conditions ph and alk move together vs when they don't.

In the mean time, I read your chem QOD thread on the list of things that precipitate out of solution when sodium silicate is dosed.
I'm adding a largish amount (up to over 80 drops a day and growing in 70 gal system so over 0.2ppm Si) of brightwell Spongexcel, - sodium metasilicate - and usually see a nice precipitate cloud upon addition to tank water.
Am I precipitating out measurable amounts of anything I'm tracking?

Btw, today I started mixing the Si drops into distilled water first about 10 ml per drop, and no clouds upon addition to tank. Precipitation avoided? Or just concealed?

 

[Randy Holmes-Farley]

I'm new to measuring pH, I need to re read to get a better grip on what ph changes signify in connection with other nutrients, and under what conditions ph and alk move together vs when they don't.

In the mean time, I read your chem QOD thread on the list of things that precipitate out of solution when sodium silicate is dosed.
I'm adding a largish amount (up to over 80 drops a day and growing in 70 gal system so over 0.2ppm Si) of brightwell Spongexcel, - sodium metasilicate - and usually see a nice precipitate cloud upon addition to tank water.
Am I precipitating out measurable amounts of anything I'm tracking?

Btw, today I started mixing the Si drops into distilled water first about 10 ml per drop, and no clouds upon addition to tank. Precipitation avoided? Or just concealed?

pH and alk do not necessarily move together, but lower pH makes it harder for calcifying organisms to excrete the H+ that they removed from bicarbonate to make the carbonate that they need to deposit calcium carbonate:

HCO3- --> CO3-- (deposited with calcium) + H+ (excreted)

Sodium silicate solution is a high pH additive, and when it hits tank water, there is typically some temporary precipitation of magnesium hydroxide. It redissolves as it disperses.

 

[taricha]

Sodium silicate solution is a high pH additive, and when it hits tank water, there is typically some temporary precipitation of magnesium hydroxide. It redissolves as it disperses.

Perfect. temporary precipitation is what I was hoping for. I test, then dose - so system has about 24 hours to resettle before next testing.

While we're on Alk questions... here's a ridiculous one. My holothuria impatiens cucumber is a small Ca/Alk reactor, but how small?

"These deposit feeders process carbonate sand and rubble through their digestive tract and dissolve CaCO3 as part of their digestive process. In aquarium incubations with Stichopus herrmanni and Holothuria leucospilota total alkalinity increased by 97 +-13 and 47+-7 micromol/kg respectively. This increase was due to CaCO3 dissolution, 81 +-13 and 34 +-6 micromol/kg and ammonia secretion, 16+-2 and 14+-2 micromol/kg"
"...Because of difference in size, the S. herrmanni were incubated in 8 L of seawater while H. leucospilota were incubated in 4 L of seawater."
source: Potential influence of sea cucumbers on coral reef CaCO3 budget....

My Q is, I can't find anything on how to convert from micromol/kg of total alkalinity to dkh or meq/L or other common aquarium Alk unit.

 

[Randy Holmes-Farley]

97 umole alkalinity/kg = 0.100 meq/L = 0.28 dKH.

That said, the ammonia excretion part is not going to be retained. So just focus on the CaCO3 dissolution part.

 

[Randy Holmes-Farley]

Bear in mind that result is based on 1 of these cucumbers for each gallon or two of aquarium water, so 120 gallon tank would need a hundred to give this effect.

"Because of difference in size, the S. herrmanni were incubated in 8 L of seawater while H. leucospilota were incubated in 4 L of seawater."

 

[Randy Holmes-Farley]

Not many people keep 50 of these in a 100 gallon tank: [emoji1]

http://www.wildsingapore.com/wildfacts/echinodermata/holothuroidea/herrmanni.htm

 

[taricha]

Yep, the small guy who put out half of that calculated .28 dkh is more the size of the one in my tank (same genus too).
So 0.14 dkh in 1 gallon divided by my 70 gallon system is...
0.002 dkh. Real, but ignorably small. Good to know for certain.