Saltwater chemical depletion orders

schabiazabi · Oct 19, 2016

I'm curious if anyone ever was able to calculate saltwater tank chemical depletion orders.
I know this is a difficult question due to many variables, but maybe someone tried it on a regular SPS tank, or even an empty tank.

For example, the depletion would be on the order of x PPM per day.

saltyphish · Oct 19, 2016

That would depend entirely on what is stocked in the tank and how much. Some corals have more requirements then others. I dont see how anyone can do a ppm a day figure except for their own personal tank. Even that is subject to change with growth and loss.

Randy Holmes-Farley · Oct 19, 2016

It varies too much to give any exact values, but...

alkalinity typically depletes 0.5-4 dKH per day

for each 1 dKH of alk depletion, calcium depletes by about 7 ppm and magnesium by about 0.7 ppm.

schabiazabi · Oct 19, 2016

4 dKH per day

That is huge. I was afraid this is true. On my past LPS tank I noticed I had hard time keeping up with ALK, but I never measured exactly. It was just a nightmare doing it manually.

Anyway, let me show you what I came up with and why I'm curious to find out depletion orders.

I'm looking to build myself an ocean like tank, or I want to try at least. This time I have way more patience, and less greed. If it means keeping only a pair of wild clownish in a 250G tank, so be it. Here is the idea:

I want to rely on denitrification cycle and 5% daily water changes only. No supplementation dosing, and no equipment in the tank. No sand beds, no live rock (or just a few none pours rocks). The goal is to find a perfect balance (if possible) where 5% daily water changes alone are able to keep a stable tank and mimic ocean water parameters. I want to rely on water changes because I invented a way to do automatic water changes. More, I hope water changes will keep a better chemical balance, as oppose to selective chemical dosing.

The plan is to start with an empty tank for a while and see if water changes are enough to support coralline algae growth. If it is enough, I will add 2 corals and watch the progress. If it's working, I will add 2 fish and observe for few months. In case the water parameters are stable and going great I will add few more corals and keep observing. I may be able to find a "natural" limit for my tank and keep it below it in order to have as much resemblance to the ocean as possible.

I'm not sure if this was done before using measurements, and a more scientific way, but I have a feeling an ocean is not much different than a well balanced system. I wonder what you guys think.

Randy Holmes-Farley · Oct 20, 2016

I do not think there is any process which will add back alkalinity naturally in a reef system to boost alk adequately if you have growing hard corals or coralline algae, and 5% daily changes also won't do it. 30-50% daily would. I show that mathematically here:

Water Changes in Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2005-10/rhf/index.php

from it:

Figure 22. Alkalinity as a function of time when performing daily water changes equivalent to 0% (no changes), 15% and 30% of the total volume each month (in other words, 0%, 0.5% and 1% per day). In this example, alkalinity is present at 4 meq/L (11 dKH) at the start and is depleted at a low rate of 0.2 meq/L (0.6 dKH) per day.

Figure 23. Alkalinity as a function of time when performing very large daily water changes of 0% (no changes), 5%, 10%, 15% and 30% of the total volume EACH DAY. In this example, alkalinity is present at 4 meq/L (11 dKH) at the start and is depleted at a low rate of 0.2 meq/L (0.6 dKH) per day.

Figure 24. Alkalinity as a function of time when performing very large daily water changes of 0% (no changes), 15%, 30% and 50% of the total volume EACH DAY. In this example, alkalinity is present at 4 meq/L (11 dKH) at the start and is depleted at a moderately high rate of 1 meq/L (2.8 dKH) per day.

Cory · Oct 20, 2016

If your trying to just keep an ecosystem, where there is no food input, probably two clowns wont live long. However if you put in a mandarin goby, and had the system generate enough pods by having them eat algae the system might work.

As Randy said, alkalinty will be needed to top up

schabiazabi · Oct 21, 2016

^ I'm not trying to keep clowns with no food. I would be the only clown then.

Randy thanks for the link. I read your article. From the article it's pretty clear water changes and supplementation is the only way, but I have a question:

How does the ocean replenish itself? I know you're going to say it's big, and the reef is small, and there is no light deep down, so no calcification, but wouldn't ALK get depleted over time? Or better question, where does ALK, Calcium and Mag come from in the ocean to begin with? Is the rock releasing the chemicals?

Cory · Oct 21, 2016

schabiazabi said:
^ I'm not trying to keep clowns with no food. I would be the only clown then.

Randy thanks for the link. I read your article. From the article it's pretty clear water changes and supplementation is the only way, but I have a question:

How does the ocean replenish itself? I know you're going to say it's big, and the reef is small, and there is no light deep down, so no calcification, but wouldn't ALK get depleted over time? Or better question, where does ALK, Calcium and Mag come from in the ocean to begin with? Is the rock releasing the chemicals?

That comes from rain falling on mountains, making rivers and the rivers run into the ocean. You did say you wanted to keep two clowns

Randy Holmes-Farley · Oct 21, 2016

schabiazabi said:
How does the ocean replenish itself? I know you're going to say it's big, and the reef is small, and there is no light deep down, so no calcification, but wouldn't ALK get depleted over time? Or better question, where does ALK, Calcium and Mag come from in the ocean to begin with? Is the rock releasing the chemicals?

The ions in seawater come from many sources, including weathering of rocks on land releasing them into rivers and dust that enter the ocean, calcium carbonate dissolving in the very deep ocean due to the high pressure, calcium carbonate dissolving in sediments where the pH can be low enough for dissolution, underwater volcanoes and deep sea vents, passage of calcium carbonate through the GI tract of animals where the pH can be low enough for dissolution, etc.

schabiazabi · Oct 21, 2016

Fair enough when it comes to Calcium, but what about Alkalinity and Magnesium? Where do they come from? This is what I found on Wikipedia last night and I find it very logical:

Oceanic Alkalinity
Processes that increase alkalinity
There are many methods of alkalinity generation in the ocean. Perhaps the most well known is the dissolution of CaCO3 (calcium carbonate, which is a component of coral reefs) to form Ca2+ and CO32− (carbonate). The carbonate ion has the potential to absorb two hydrogen ions. Therefore, it causes a net increase in ocean alkalinity. Calcium carbonate dissolution is an indirect result of ocean pH lowering. It can cause great damage to coral reef ecosystems, but has a relatively low effect on the total alkalinity (AT) in the ocean.[7] Lowering of pH due to absorption of CO2 actually raises the alkalinity by causing dissolution of carbonates.

Anaerobic degradation processes, such as denitrification and sulfate reduction, have a much greater impact on oceanic alkalinity. Denitrification and sulfate reduction occur in the deep ocean, where there is an absence of oxygen. Both of these processes consume hydrogen ions and releases quasi-inert gases (N2 or H2S), which eventually escape into the atmosphere. This consumption of H+ increases the alkalinity. It has been estimated that anaerobic degradation could be as much as 60% of the total oceanic alkalinity.[7]

and specifically these two sections:

Denitrification and sulfate reduction occur in the deep ocean, where there is an absence of oxygen. Both of these processes consume hydrogen ions and releases quasi-inert gases (N2 or H2S), which eventually escape into the atmosphere. This consumption of H+ increases the alkalinity.

and

It has been estimated that anaerobic degradation could be as much as 60% of the total oceanic alkalinity.

Alk in the ocean is not dosed, and the ocean is not a "storage" of Alk that gets depleted. Alk in the ocean is consistent, because there are processes that produce it. This leads me to believe, denitrification in the sand bed is the only think "big enough" in the ocean that could keep up with Alk depletion ratios you posted. Therefore I sort of feel like a novice reefer in the 80's who just discovered the Deep Sand Bed method. But don't give up on me just yet, because I have some valid question related to this.

1. How hard would it be to verify the production of Alk by denitrification in the reef setup? All it takes is two identical 20G tanks, one with no send bed at all, and the other one with a 200 gallon container/sump full of send deep to about 4 feet, with no access to light. Then we could chart Alk depletion and compare the two graphs. If the theory is correct, a 1 to 10 ratio of display tank to send bed should show major Alk production.

2. Why is it recommended to have a send bed be no deeper than 6 inches? Ocean's sand bed is way deeper and functions exactly like a deep send bed in the tank. (I agree sand bed should not be in the display tank, but in a remote container where there is no light and no organic waist being collected. It has to function just like send bed in the ocean).

Randy Holmes-Farley · Oct 22, 2016

I'm not sure of your primary point, but my mechanisms apply to alk too.

Denitrification does produce alk, BUT ONLY the same amount of alk that was depleted when the organics and ammonia were converted into nitrate in the first place. There is no net gain ((or loss) ir alkalinity by these transformations (except sulfur denitrification, which is a net loss of alkalinity.

Sand beds deeper than 6 in are likely just a waste of space, unless the pore size is big. Its not like anything bad happens in deeper regions that we are wanting to prevent.