Vodka dosing finally kicked in; now what?

[boobookitty]

I have a 400G mixed reef, started 3 years ago after retiring my 240G reef, and since zeovit was successful on the 240G, I used it on this one. Unfortunately this time around zeovit wasn’t useful; I do have a higher bioload than the previous tank, and over a period of a couple years nitrates and phosphates crept higher and higher. Tank health was decent so I didn’t worry, but after a couple years it started to take its toll (diminished coloring and growth, etc.)

So I abandoned zeovit and began vodka dosing, following the method described by Walton/Bjornson in Reefkeepng magazine. When I started dosing back in December, nitrates were between 50 and 100, and phosphates were 1.5+. I followed the method to the letter for the first several months, but when I got no results at all after 4 months I started increasing the dosage more, and at the end was up to 2 ml/day. Good thing too; if I’d stuck to the original dosing it would have taken me 3.7 years to finally see results.

So finally, FINALLY, in the past two-three weeks the vodka dosing kicked in. It started when dosing was around 95 ml/day, but phosphates (my primary testing, since the Hanna gives digital results) really bounced around quite a bit at first, dropping then rising back up, then dropping again, so I didn’t know if it was working or just an anomaly and continued to increase the dosing during that period (it’s now 120ml/day). I would see drops, then over a couple days phosphates would bounce back up, then start going down again. I’m guessing it has something to do with their being leached out of the rocks; my phosphates and nitrates were pretty high for a couple years as I kept waiting for zeovit to take care of the problem.

Along the way the last 7 months I’ve tested phosphates daily, nitrates sporadically. Phosphates started out at around 1.5, then dipped to 1.35 and 1.15 where they plateaud at each level for a while. Then dips down to 0.95, then back up to 1.15, then finally a series of drops down to 0.75 today. I checked nitrates a few times along the way, and I could see some progress down as well (they started at 50+).

So I finally checked nitrates again today: they’re undetectable on the Salifert kit. Which is great, but now I’m wondering what will happen with the phosphates. From what I understand phosphates and nitrates come down together with vodka dosing, but with nitrates effectively at zero does this mean phosphates will stop going down? Should I cut back to maintenance dosing now (half of current dosing), since one of the two parameters has zeroed out?

[mcgyvr]

Now you dose nitrates to allow phosphates to drop further.. Or just run GFO..
Or look at your tank.. Are you having problems because of these numbers (nuisance algae)? If not why lower it.. There is no "magic" number and many tanks do great with levels far in excess of whats commonly spouted as the truth around here..
Interesting video..
https://www.youtube.com/watch?v=ZRIKW-9d2xI

[reefgeezer]

I believe the standard process is to cut the dose in half once nitrates hit 0. This is the "maintenance dose". The theory is you can adjust the dose to keep nitrates where you want them. I never could though and have to dose nitrates every once in a while.

It may be difficult to reduce what is a fairly high concentration phosphates using carbon dosing. GFO might be the best approach to reduce them to the level you desire. Once there, carbon dosing may maintain it if you can keep the process from becoming nitrate limited.

There is disagreement about acceptable phosphate levels. FWIW, .03 to .09 ppm is the range I shoot for.

[boobookitty]

0.03 would be a dream at this point. Really uncomfortable dosing nitrates: I’m old school, 20+ years reefing, from the era when we worked our asses off to get nitrates to undetectable. . Phosphates were 0.75 again today; I’ll keep the increasing going throughout the weekend to see if that changes or if phosphate doesn’t move. If it’s the latter I’ll move to maintenance dosing and figure out what to do to lower phosphates more.

[mcgyvr]

So are you having problems or just chasing numbers?

[boobookitty]

Problems. With nitrates between 50 and 100, and phosphates around 1.5, I started having serious issues with coral coloration and growth, and some stn.

[reefgeezer]

Originally Posted by boobookitty

0.03 would be a dream at this point. Really uncomfortable dosing nitrates: I’m old school, 20+ years reefing, from the era when we worked our asses off to get nitrates to undetectable. . Phosphates were 0.75 again today; I’ll keep the increasing going throughout the weekend to see if that changes or if phosphate doesn’t move. If it’s the latter I’ll move to maintenance dosing and figure out what to do to lower phosphates more.

Sounds like a good plan.

[Vinny Kreyling]

Phosphates & Nitrates are tied together in that they are removed together in a ratio.
-0- Nitrates & phosphate will need GFO for removal, or dose nitrates.
Redfield Ratio comes to mind.

[boobookitty]

They didn’t come down in the Redfield ratio though: nitrates dropped over 50 ppm while phosphates dropped 0.75 ppm. Definitely not 12-1.

[bertoni]

The Redfield Ratio is for phytoplankton in the ocean. It doesn't necessarily work for anything else, and there's likely not much phytoplankton in a tank.

[Vinny Kreyling]

Thanks Boss for the clarification.

[madweazl]

Carbon dosing isnt very affective at removing phosphates to begin with so you'll want something else to tackle that with. Increasing your dose isnt going to accomplish anything positive so cut that back to where you're seeing some nitrates again and then start to fine tune that.

If you have a refugium, ATS, etc., you can tackle the phosphates that way. If not, something like GFO will need to be used.

[Dan_P]

Originally Posted by bertoni

and there's likely not much phytoplankton in a tank.

How are you defining phytoplankton? I may want to arm wrestle you on the above statement :-)

[Dan_P]

The recommendation to drop to half the dosage or any dose doesn’t seem to make sense in light of why you dose in the first place. If you dose to consume nitrates, you should not need to dose if there are no nitrates to consume.

Wouldn’t you want to determine if the system is still producing nitrates in excess of the system’s non-fed denitrification capabilities by ending carbon dosing (either stopping or rapidly rampling down) and monitoring nitrates for a few weeks, resuming carbon dosing only if necessary?

By the way, I have been dosing calcium acetate (vinegar basicified with solid kalkwasser) to my 50 gallon fish only system, increasing the dose stepwise and observing the system for 4-8 weeks after each increase of daily dosing. I started in December and just went to 0.5 mL/gal per day. I plan to get to high dose by December and report back on my observations. I am also running small scale experiments and may have results by then as well.

[reefgeezer]

Originally Posted by Dan_P

The recommendation to drop to half the dosage or any dose doesn’t seem to make sense in light of why you dose in the first place. If you dose to consume nitrates, you should not need to dose if there are no nitrates to consume...

Hi Dan. I believe the reduction of the carbon source is an attempt to manage the nitrates that the system will produce. Establishing a dose that holds nitrates at a desired level is kind of trial and error from there.

IMHO, maintaining the current dose or abruptly discontinuing the dose are not desirable options. More carbon won't help if there are not enough free nutrients to allow for bacterial propagation or formation of organic compounds. Stopping the dose altogether might allow more toxic nitrogen compounds to spike while bacteria levels readjust.

As we've discussed about before, we really don't know exactly how this process works. I hope you experiments might provide some definitive results.

[Dan_P]

Originally Posted by reefgeezer

Hi Dan. I believe the reduction of the carbon source is an attempt to manage the nitrates that the system will produce. Establishing a dose that holds nitrates at a desired level is kind of trial and error from there.

Hi John, this seems reasonable. What are the assumptions that leads one to propose that the system needs carbon dosing after removing the accumulated nitrate?

IMHO, maintaining the current dose or abruptly discontinuing the dose are not desirable options. More carbon won't help if there are not enough free nutrients to allow for bacterial propagation or formation of organic compounds. Stopping the dose altogether might allow more toxic nitrogen compounds to spike while bacteria levels readjust.

I see your points. Caution seems to be warranted. Again, there are some underlying assumptions which might need to be reconsidered. Nitrate is not the only nitrogen compound available for bacteria to assimilate. What would be the harm in continuing to dose carbon and letting the bacteria switch from nitrates to ammonia and nitrogen containing organics that are always present in the aquarium? On the other hand, an established biofilter (aka, cycled aquarium) will convert ammonia to nitrate. What is behind the assumption that the aquarium has become “uncycled” or the biofilter impaired enough to cause a spike in ammonia if the carbon dosing is stopped?

As we've discussed about before, we really don't know exactly how this process works. I hope you experiments might provide some definitive results.

Me too John! I find these debates useful in designing experiments. My questions above about assumptions are stimulants for further debate.

[bertoni]

Originally Posted by Dan_P

How are you defining phytoplankton? I may want to arm wrestle you on the above statement :-)

I think of phytoplankton as photosynthetic (autotrophic) plankton.

[boobookitty]

My understanding is that cutting off the carbon supply suddenly will kill the bacterial population that has been built up, causing an large drop in oxygen and potentially killing a lot of stuff. Is that not accurate?

[reefgeezer]

Originally Posted by Dan_P

Hi John, this seems reasonable. What are the assumptions that leads one to propose that the system needs carbon dosing after removing the accumulated nitrate?

The assumption is that the system will continue to produce the same quantity of nitrate that resulted in the accumulated levels & some mitigation would be required. How much is an unknown so trial & error is needed.

Originally Posted by Dan_P

Nitrate is not the only nitrogen compound available for bacteria to assimilate. What would be the harm in continuing to dose carbon and letting the bacteria switch from nitrates to ammonia and nitrogen containing organics that are always present in the aquarium? On the other hand, an established biofilter (aka, cycled aquarium) will convert ammonia to nitrate. What is behind the assumption that the aquarium has become “uncycled” or the biofilter impaired enough to cause a spike in ammonia if the carbon dosing is stopped?

Great questions. I wish I had the answers, but I'm just not that smart.

I don't understand the bacteria propagated by carbon dosing well enough to even make a guess. I don't even know if the bacteria directly assimilate the the nitrogen compounds or if adding the carbon creates more complex organic compounds that include the nitrogen (and phosphate) that the bacteria then assimilate. I don't know if the bacteria propagated in the presence of nitrate would "switch over" to other compounds. What scares me the most is I don't know what happens to the free carbon if other nutrients limit the assimilation process.

I don't think the substrate will become un-cycled, but at the same time I am afraid that the populations of denitrifying bacteria may be lower where carbon dosing is occurring.

I need to stipulate here that I only add about 8ml of vinegar a day to my tank now & even dose nitrates every once in a while. Once the level was reduced to 0, I had trouble keeping nitrates detectable so the dose slowly dwindled to nothing. What I add now (in my theory anyway) is increase DOC and biological diversity. My corals seem to do better when a little vinegar is added and definitely have better color with detectable nitrate levels. I am at a loss to explain either outcome though. It's interesting that my system is a simple Berlin Method tank with a good skimmer. It has a decent bioload. Except for some algae I allow to grow in the overflow, I can't explain what's keeping nitrates low. Sometimes it's just better to be lucky than smart!

I do look forward to the results or your experiments and the observations made.

[reefgeezer]

Originally Posted by boobookitty

My understanding is that cutting off the carbon supply suddenly will kill the bacterial population that has been built up, causing an large drop in oxygen and potentially killing a lot of stuff. Is that not accurate?

I think that's not likely. If your skimming, much of the bacteria is being removed. The bacterial population will decrease, but a mass die off wouldn't happen. It would just slowly dwindle as it's food source disappeared. Ammonia spikes would be my concern, though I'm not sure it would happen.

I think the dose reduction is just the first step in determining how much carbon is need to maintain desired levels. It could be that there would be not impact to just stopping. IMO, more importantly, nothing should ever be done all at once in a reef tank.

[Dan_P]

Originally Posted by bertoni

I think of phytoplankton as photosynthetic (autotrophic) plankton.

Reef tanks don’t have diatoms, dinoflagellates, cyanobacteria, etc. floating in the water? To be fair, I should have also asked how many of these things per mL do you think are floating around that you consider not many.

For my fish only system, I count 25-100 dinoflagelates per mL and 25 diatoms per mL. That’s just two species, presumably photosynthetic by their color. There are more of the “other” green and golden brown things. I get the count by centrifuging 500 mL tank water at 4000 rpm for ten minutes and resuspending the pellet in a small known amount of tank water for a count. This could even be an underestimate because of the short centrifuge time. My tank’s skimmate contains tens of thousands per mL.

So was your estimate based on gut feel or do you know of someone actually counting the organisms in a reef system?

[Dan_P]

Originally Posted by boobookitty

My understanding is that cutting off the carbon supply suddenly will kill the bacterial population that has been built up, causing an large drop in oxygen and potentially killing a lot of stuff. Is that not accurate?

Bacteria are not so easily killed for one thing (if it helps, Randy doesn’t think so either). For another, they may not die like multicellular organisms, that is drop dead and decompose. For example, they might form spores. In an event they will slow down their metabolism first and continue to maintain their internal machinery as long as possible. In the mean time, predation by protozoa, nematodes, etc. and death by phages would continue as during dosing but now with the effect of a population reduction.

By the way, if you accept that carbon dosing works because of biomass formation and exporting through skimming, there won’t be much bacteria sludge or floc around to be effected by a sudden decline in a carbon source. If that’s wrong, then there willl be slime, floc or sludge left behind that will be disappointed but probably not drop dead.

A large drop in oxygen occurs from a large amount of metabolic activity, like from carbon dosing or a lot of organic matter decomposing, not from a couple of grams of bacteria suddenly dying (which they probably won’t) and being consumed by other bacteria, protozoa and sponges.

I plan on a complete, all at once shut down on dosing when I reach the maximum level in December.

[Dan_P]

Originally Posted by reefgeezer

I think the dose reduction is just the first step in determining how much carbon is need to maintain desired levels. It could be that there would be not impact to just stopping. IMO, more importantly, nothing should ever be done all at once in a reef tank.

I agree John.

[bertoni]

Originally Posted by Dan_P

Wouldn’t you want to determine if the system is still producing nitrates in excess of the system’s non-fed denitrification capabilities by ending carbon dosing (either stopping or rapidly rampling down) and monitoring nitrates for a few weeks, resuming carbon dosing only if necessary?

Ending carbon dosing immediately might be fine. We don't have useful data on what might happen, though. If you just want to know whether the tank is producing nitrate, then dropping the carbon might tell you that, but various organisms might react badly, at least in theory.

[bertoni]

Originally Posted by Dan_P

Reef tanks don’t have diatoms, dinoflagellates, cyanobacteria, etc. floating in the water? To be fair, I should have also asked how many of these things per mL do you think are floating around that you consider not many.

For my fish only system, I count 25-100 dinoflagelates per mL and 25 diatoms per mL. That’s just two species, presumably photosynthetic by their color. There are more of the “other” green and golden brown things. I get the count by centrifuging 500 mL tank water at 4000 rpm for ten minutes and resuspending the pellet in a small known amount of tank water for a count. This could even be an underestimate because of the short centrifuge time. My tank’s skimmate contains tens of thousands per mL.

The topic in question is dissolved nutrient reduction, so I would be more specific by saying I don't believe that phytoplankton does much in the way of filtration. My belief here is based on the lack of any nutrient response to a new UV unit appearing on a system in any case of which I'm aware.