Monitoring Organic Carbon With Bleach

[Dan_P]

I wanted to share my observations using bleach, i.e., chlorine, to monitor the level of organic compounds in my 40 gallon fish only aquarium. The test involves adding a known amount of chlorine (bleach) to a sample of aquarium water and measuring the chlorine concentration after 24 hours with a Hanna Total Chlorine Checker. Chlorine reacts with a wide range of organic molecules and is especially reactive with ammonia and organic amines. Chlorine consumption is not a replacement for TOC measurements but correlates with it and UV measurements of organic molecules in water. My primary interest is to monitor organic compound levels to determine when to change GAC and to determine the value of increasing or decreasing the amount used.

I made measurements on aquarium water over the last several months. During this time, I changed the GAC three times, ramped up carbon dosing (acetate), abruptly ended carbon dosing, attached a new 75 gallon aquarium to the system and removed the old 40 gallon aquarium (first 3 red “X’s” in graph below are associated with adding the new aquarium).

In the plot, dashed red lines indicate the chlorine demand 24 hours after replacing the GAC. After the first two changes, chlorine demand continued to decline and then slowly increased. After the third GAC change, I abruptly stopped dosing acetate (green dashed line is the carbon dosing regime during this time) to see what would happen to the nitrate level (another post). Shortly after the usual decline in chlorine demand after a GAC change, it peaked and slowly declined. Whether the system change (harvesting moribund looking macro algae from the refugium) had anything to do with the decline is a mystery.

My plan is to continue measuring chlorine demand once a week to monitor GAC performance and to look for interesting trends. By the way, the chlorine demand of wet skimmate is about 30 X greater than the aquarium water.

 

[NY_Caveman]

Very interesting. Thanks for sharing.

 

[taricha]

That's cool. Looking at that data, I'd say if I was trying to run a pretty tight ship with regards to GAC, looks like change about every 30-40 days.
more frequent than that looks unhelpful.

Thinking about that spike after stopping the carbon, if I understand what's being measured, I can think of a few possibilities - no idea which of these is likelier:

• ammonia (or nitrate etc) increased
• Something died, releasing organics - maybe that something is the bacteria fed on carbon
• stopping carbon dosing caused bacterial assemblages on substrates to break up and appear in the water column
• paradoxically, the bacteria in the water column were consuming organics and keeping them low. The cutoff of carbon led to decrease in bacteria in the water and thus a reduction in consumption of water-borne organics.

Side question, I wonder if this method could detect coral chemical warfare, or toxins from dinoflagellate outbreaks or other large molecule marine biotoxins?

 

[Dan_P]

That's cool. Looking at that data, I'd say if I was trying to run a pretty tight ship with regards to GAC, looks like change about every 30-40 days.
more frequent than that looks unhelpful.

Thinking about that spike after stopping the carbon, if I understand what's being measured, I can think of a few possibilities - no idea which of these is likelier:

• ammonia (or nitrate etc) increased
• Something died, releasing organics - maybe that something is the bacteria fed on carbon
• stopping carbon dosing caused bacterial assemblages on substrates to break up and appear in the water column
• paradoxically, the bacteria in the water column were consuming organics and keeping them low. The cutoff of carbon led to decrease in bacteria in the water and thus a reduction in consumption of water-borne organics.

Side question, I wonder if this method could detect coral chemical warfare, or toxins from dinoflagellate outbreaks or other large molecule marine biotoxins?

I agree on the 30-40 day lifespan. I still need to how far down and for how long I can push the Cl2 demand and whether just using 2X the amount of inexpensive Marineland carbon is the same thing as 1X ROX. I saw the BRS video on GAC comparisons and that was my feeling.

Unfortunately, the spectrometer was in for warranty repair, so no NH3 test. I will post the other tank parameters along with carbon spike data under a post about the abrupt halt of carbon dosing. I didn’t too make an overly complex post.

I will attempt to repeat this chlorine demand spike to confirm that it was not a one time event.

Because I do not fllter the sample water, the sample contains dissolved and particulate organics. Either or both of your suggestions about a pulse of organic carbon or bacteria going into the water could be the answer. I see this peak to a lesser degree with KMnO4 demand, so it’s real. I need to consider filtering the sample.

Along your line of thinking, the bacteria that were enjoying the acetate meals were themselves consumed when they passed on to bacteria heaven after the free lunch stopped. One thing is certain. I don’t have to scrape the glass as nearly as often now that I stopped dosing. As a reminder, in small scale dosing experiments, acetate can be consumed with little or no nitrate consumption. I wonder whether dosing is mostly about giving a free lunch to aquarium bacteria and just a little for nitrate nitrate reduction.

Could Cl2 detect chemical warfare? Depends on the toxin’s structure. At this point I do not have a quantitative sense about the sensitivity of Cl2 demand.

 

[taricha]

Along your line of thinking, the bacteria that were enjoying the acetate meals were themselves consumed when they passed on to bacteria heaven after the free lunch stopped. One thing is certain. I don’t have to scrape the glass as nearly as often now that I stopped dosing. As a reminder, in small scale dosing experiments, acetate can be consumed with little or no nitrate consumption. I wonder whether dosing is mostly about giving a free lunch to aquarium bacteria and just a little for nitrate nitrate reduction.

Interesting that bacteria can consume acetate out of balance relative to N and P. That's not something one normally sees with N or P. The mechanisms for reducing either of them usually require or at least are aided by the presence of others. Maybe Carbon doesn't need N or P to get eaten but N&P need each other and some carbon.

Could Cl2 detect chemical warfare? Depends on the toxin’s structure. At this point I do not have a quantitative sense about the sensitivity of Cl2 demand.

Here's a table of concentrations of sodium hypochlorite needed to totally inactivate a list of toxins - from a pdf on lab toxin procedures. I highlighted four of them that I'm aware of being made by dinoflagellates.

Does these being inactivated by chlorine imply a chlorine demand?
Does the fact brevetoxin requires ~25x times more NaOCl than palytoxin tell us anything about their relative chlorine demand?

 

[Dan_P]

Here's a table of concentrations of sodium hypochlorite needed to totally inactivate a list of toxins - from a pdf on lab toxin procedures. I highlighted four of them that I'm aware of being made by dinoflagellates.

Does these being inactivated by chlorine imply a chlorine demand?
Does the fact brevetoxin requires ~25x times more NaOCl than palytoxin tell us anything about their relative chlorine demand?

Yes, inactivation suggests that bleach is reacting with these toxins. I looked up the structures and all contain multiple potential sites of reaction with chlorine. I would expect a chlorine demand. The table of amounts of bleach for inactivation might be a starting point for a chlorine demand order. The criterion of inactivation might require more bleach than just detecting each toxin molecule.

 

[Dan_P]

Interesting that bacteria can consume acetate out of balance relative to N and P. That's not something one normally sees with N or P. The mechanisms for reducing either of them usually require or at least are aided by the presence of others. Maybe Carbon doesn't need N or P to get eaten but N&P need each other and some carbon.

The discussions that we usually have about carbon dosing neglect respiration and focus on biomass generation. Bacterium needs energy just to maintain itself and keep the machinery working. It needs nitrogen and phosphate to increase the population, to make biomass, but just to hang around, maybe not so much. I have observed at small scale phosphate consumption along with acetate consumption, presumably for ATP synthesis and/or stocking up while there is an abundance.

I dosed the aquarium today to confirm that I can monitor acetate levels.