How do you measure nutrient levels?

[Palting]

Nitrate/Phosphate are the old measures. High nitrate/phosphate equals high nutrient levels, and vice versa. How about "adequate" nutrient levels? Nitrates are the end result of decomposed or processed nutrients, so they can't be a good measure. Especially if you have mechanisms in place for nitrate export, like a ton of macroalgae for example.

I know my tank nutrient levels have been low. SPS love it, but softies and LPS don't. For the last month or so, I've been dumping phytoplankton, zooplankton, Mysis, Coral Frenzy once a week. I turn all pumps and powerheads off, target feed, tank gets really cloudy with all that food in it, then turn everything back on again after 15 minutes or so. Duncans and candycanes puff up, mouths open up, so I know I'm doing something. Is it enough? Is it too much? Do I just observe and wait until either the softies/LPS show growth or the the SPS wilt/develop STN? Whatever nitrate export I have seem to be handling the load, since nitrates continue to be zero or undetectable, so I'm left with this :hmm4:

 

[reefgeezer]

I've taken to observing the tank IN ADDITION to testing. The condition determines what I do for maintenance. For example: If I see a little algae start on the glass, or if my SPS start to brown, I add a little more vinegar, GFO, and maybe add a few gallons to the weekly water change. If the algae starts to disappear or SPS start to fade, I reduce the vinegar and GFO and revert to my normal 10% weekly water changes... or if I haven't elevated the vinegar or GFO I just feed more. I don't however, reduce feedings or turn off the skimmer.

I believe a lot of problems start with elevated dissolved organics, so to me it is a nutrient. Not that I measure it directly, but I manage the tank to minimize it I can tell the organic levels are rising by how long bubbles that build up in my bubble trap to bust, by looking through the tank and evaluating the degree of yellowing, and by looking at the surface in the corners of the DT.

 

[danil]

It's nice you divide Nutrients and Nitrate levels. I'm with you on it. Though many think it's the same and some even try to dose nitrate in form of Potassium Nitrate to feed their corals in attempt to 'fix' their lack of nutrients issue. It is possible to have enough nutrients for corals and very low or undetectable nitrate level. Good examples are established ULNS tanks with thriving corals. So answering your question - I don't think you are doing right thing dumping all of the above into your tank. Though I support the idea of feeding corals I believe most of these stuff is just a pollution in your tank. I would stick with one supplement and watch your corals or even better tune up nutrients level in your tank through fish population. It's not a myth corals readily accepted fish waste along with some left over food particles so having right amount of fish and feeding them right amount of food can solve any nutrient issue.
SNT/RTN of SPS corals is different issue. 90% of the time it's related to Alk level being unstable, too low, too high or unappropriated for given nutrient level. Keep it stable in recommended range and you'll be fine. Colors is another thing though but it's out of the scope for this thread. GL.

 

[Palting]

Thanks for the responses. My point, though, is that there must be an objective measurement of some kind. I'm trying to find out if there is one.

For 3 years, I've fed my fish so that they are healthy and growing, as well as pooping . I have tangs, and boy they make large poop. I also have quite a bit of fish, and have actually been told I have too much. So, adequately feeding fish does not seem to be a good enough measure for coral feeding. Corals that prefer low nutrient, like the SPS, are thriving in my tank, but coral higher requiring nutrient levels seem to be just surviving.

I do keep an eye on the coral. I've cautiously upped the coral feeding, and there seems to be some response from some. Feeding responses as I noted in the first post, as well as zoas reappearing where whole colonies disappeared in the past. So, I know I'm on the right path to achieving that happy middle ground of nutrient level, where both SPS and softies thrive. What I don't know is if I'm there yet, or have I overshot it. Hence, my question: Other than observing for positive or, heaven forbid, negative effects on the coral, is there an objective measurement, and is there an ideal number for this measurement?

 

[Eric45]

I find .03 ppm a generally accepted measurement for the maximum amount of PO in a reef tank after which algae will begin to grow. I use a Hanna PO checker which I find to be reliable in measuring PO.

 

[reefgeezer]

There are test kits for dissolve organic carbon or total organic carbon... I don't remember which... maybe both. Unfortunately I don't know what the magic number would be and I think the test kits are expensive. ORP might also give you a clue. If I remember correctly, approaching 400 is great.

I think if dissolved organics are low (thus higher ORP) nitrates and phosphates will not build as quickly.

 

[Palting]

I may get the Hanna phosphate checker. One can't have too many toys . How do you check ORP, John?

 

[reefgeezer]

How do you check ORP, John?

ORP meter, but they are not cheap and have to be calibrated regularly. Many people that use ozone use them. You didn't say cheap or easy. You just said "objective". :lol2:

 

[Palting]

ORP meter, but they are not cheap and have to be calibrated regularly. Many people that use ozone use them. You didn't say cheap or easy. You just said "objective". :lol2:

LOL!! Guess I didn't. At least now there is a choice. Thanks!

 

[Signal151]

The ultimate way would be to test for total dissolved organic carbon. Here is a technical paper on the test. Browse down to #2, the summary...

"2.1 The Shimadzu TOC-5000/5000A uses a high temperature combustion method to analyze aqueous samples for TIC, TOC and non-purge-able organic carbon (NPOC).
2.2 NPOC samples are treated with hydrochloric acid and sparged with ultra pure carrier grade air to drive off inorganic carbon. TOC samples are injected directly onto the catalyst bed with no pretreatment. High temperature combustion (680ΕC) on a catalyst bed of platinum-coated alumina balls breaks down all carbon compounds into carbon dioxide (CO2). The CO2 is carried by ultra pure air to a non-dispersive infrared detector (NDIR) where CO2 is detected.
2.3 Samples for inorganic carbon (TIC) are injected directly into a receptacle of 25% phosphoric acid where the carbonates are reduced to CO2 and detected by the NDIR."

I wonder if Salifert makes a hobby version of this test... .

Regarding ORP, I'm no expert but I've never heard it used to directly measure for DOC. In my experience, ORP is generally used by those who run ozone to assist them in not overdosing. So many factors affect ORP that it can be impossible to determine the cause if/when your ORP reading changes. It will let you know something has changed but it's not going to tell you exactly what that change has been, or if the change is cause for concern or not. There is also the issue of cause and effect. Is low ORP the cause of a cyano outbreak or is the cyano outbreak the cause of the low ORP? Of course it's been years since I last looked at ORP use in marine aquaria so perhaps the industry has made a lot of progress recently. Also, I've never used an ORP meter personally so take that for what it's worth.

Ultimately I feel the people who advise you to watch your system over time are on the right track. Make small changes then give the corals time to react. They will show you whether your action was positive or negative.

 

[reefgeezer]

Signal151 is right. I didn't mean to imply that ORP was a direct measurement. There are many factors that affect it: water changes; ozone and chemicals with with high oxidation potential (peroxide, chlorine, etc.); and etc. However, (I think) when all other things are equal, as DOC rises a drop in ORP should be observed.

You could also measure continuity. Pure saltwater at a given salinity has a different resistance than salt water of the same salinity with a high DOC level. Again, not a direct measure. I don't know what number would be significant though.

Posting this same thread in the Chemistry Forum might get some better answers.

 

[Palting]

Thanks again. There seems to be some positive response to the current ramped up level of feeding, so I think I'll just stick to observing thigs for the next 4-6 weeks to make sure the positive results are real and progressive. If not, I'll ramp it up again a little. Besides, I fear posting at the chemistry forum due to what "toys" they may recommend. It's like someone who wants to stay off sweets but goes to the best candy store in town anyway .

 

[danil]

I'm sure you've made right chose. Observing is a key. All these numbers are meaningless
for mature reef unless you can see dynamic and make fine adjustments. Its a really fine line to balance the system and commonly it's within test error range. I would still get Hanna for phosphate though . Also have you try oyster feast?

 

[Signal151]

I did some more thinking on this issue, especially regarding the coloring of the water as dissolved nutrients build up. I found a scientific method of determining the clarity, or color of the water. It's a "Color of Water" Hanna Checker.

Click

Now, the measuring scale used is PCU (Platinum Cobalt Units) and I have no idea of what a healthy range would be for a marine aquarium. Or would there even be such a thing? I do like to keep my tanks crystal clear, so clear that it looks like my fish are suspended in air. This meter represents a method to assign a meaningful value to the clarity of one's water. Similar to monitoring ORP, a change in your water's PCU value could signal a change that you may want to be aware of. More to the point, all else being equal, such as turbidity, phosphate and Nitrate levels, an upward trend in the PCU value could possibly be linked to a rise in dissolved organics. Indeed, enough trial and error could lead to a mappable relationship between the PCU value and the level of dissolved organics?

One use I can think off right off the bat is to use the meter to scientifically test whether your new UV sterilizer or canister is indeed creating clearer water for you.

Food for thought anyway... I may have to pick up on. One can never have too many toys in this hobby. The nice thing is there are no reagents outside of having some quality RO/DI water on hand. So the cost of use is almost nothing.