Devistation

[Mermade]

Yesterday I woke up to find all my fish dead in my 50g(185litre) Clam Lagoon, I was devistated as you can imagine. Everyone was happily swimming around the night before and not so happy the next day. Amazing enough only one fish survived, to my amazement was the firefish which I named MACO.
I need help to try and find the problem. I have a theory. The tank is highly stocked with clams(18x2-3inch assorted, 1x11inch squamosa, 1x5inch maxima), no coral and few invert's. I know the tank is perhaps overstocked but take the necessary action to ensure water parameters are constant. I feed heavily, 2 water changes p/w, dose with KentCB parts A&B. The only thing I did different the previous night was to turn off the skimmer as the pump slipped blowing bubbles from the top of the skimmer so decided to fix in the morning. The only other change was the pump, normal pump is 1100 litres per hour but the impellar broke so had to use the 800 pump. I believe I need more water circulation but according to Daniel Knop(clam expert) "the rule of thumb" when keeping many clams half the amount of pump strength is only required bacause of their preference to slow currents.
What is everyone's opinion. I think that the fish died of suffocation because as maybe the clams zooxanthellae(being the greedy little creatures they are)that synthesize oxygen depleted the oxygen levels in the tank. All the clams are fine and doing great after the death of their inmates. I know it sounds silly but maybe the clams killed the fish?
Very unhappy.
Tehlia.

 

[ATJ]

Tehlia,
(Reply attempt 2)
Very sad news indeed.

You do have a lot of clams in that tank. Under light, the clams will be producers of oxygen, as you point out. In the dark, however, they will be active consumers as will most organisms. With decreased circulation, a much lower surface area of water in contact with air due to the skimmer being off and a high consumption of oxygen by the clams, your suffocation theory looks pretty accurate.

In a normal tank (without so many clams) you probably would have been OK without the skimmer. Similarly, if you had good circulation with surface agitation, things would have been OK, too. I think it is the unfortunate combination of events that led to the demise of the fish.

Another possible theory is a lowering of the pH due to higher dissovled carbin dioxide concentrations. However, fish are usually pretty tolerant of low pH.

As I said, very sad news. I hope little MACO does OK.

 

[ATJ]

Tehlia,
Oh, yeah... the clams were probably OK as they would have a lesser requirement for oxygen than the fish.

 

[Alice]

Tehlia;

I'm so sorry about your fish

The oxygen theory does fit but just to play devil's advocate I'll ask if you had any sea cukes or such that could have poisoned the vertebrates but not harmed the invertebrates?

~Alice

 

[Eric Borneman]

Oxygen level theory a posisbility. Is there an overflow in the tank and was the surface being rippled a lot by the remaining pump? I'm not sure clams will net produce oxygen as it may be used by the clam, but they are certainly going to net consume especially at night.

Eric

 

[Mermade]

Eric,
There is no overflow but yes the surface of the water was rippled. Do you think the 800w/p/litre powerhead is providing a strong enough current? Also what are the reactions that oxygen have with water(day & night) for flucuations in oxygen levels to happen. My chemistry background is nil.
Tehlia.

 

[Mermade]

Eric,
Another thought. I'm reading AC(catching up) and on page 74, discussing "chemical weaponry" in sponges. A few days ago I had a sponge overgrowing three of the clam shells, so much that the mantles were not fully expanded so I attacked them with caustic soda while I was killing the aptasias. I noticed that you mention "sponges in aquarium experiments produce increased oxygen consumption,decreased photosynthesis....". Could this have been a cause?
Tehlia.

 

[ATJ]

Tehlia,
There really aren't any chemical reactions of oxygen in water as such, it just dissolves. Given enough circulation and surface area of water in contact with air, the dissolved oxygen in the water will reach equilibrium. the equilibrium is based on the temperature of the water and the partial pressure of the oxygen in the air. The warmer the water, the lower the saturation point for dissolved oxygen. The lower the partial pressure of oxygen, the lower the saturation point. Over the practical temperatures for our tanks, and the partial pressure of oxygen we would normally experience, you won't see that much change in the saturation point for oxygen.

Note: the partial pressure of oxygen in normal air is around 20% of the air pressure. At sea level this will be close to 0.2 bar.

Oxygen dissolves in water at the air/water interface. The speed at which the oxygen dissolves is based on the partial pressure of oxygen and the area of the interface (the surface area of the water). Various things will maximise this surface area:
* an overflow
* a powerhead directed at the water surface
* the bubbles in a skimmer

Once oxygen dissolves in the water, the water needs to be circulated to move the oxygenated water around. Without circulation, diffusion is the only way that the oxygen will move through the water and this is very slow and the rate is exponential. Beyond around 2.5 cm you will get very little diffusion at all.

Therefore, to keep a tank well oxygenated you need both a large surface area in contact with the air and circulation to move the oxygenated water away from the surface and the water with less oxygen to the surface so more can dissolve.

The day/night cycles are biological. Respiration (which all organisms do) consumes oxygen. (Denitrifying bacteria use oxygen from nitrite and nitrate rather then free oxygen.) Photosynthesis generally produces oxygen. Generally, photosynthetic organisms produce more oxygen than they consume, while they are photosynthesising. However, at night they only respire and so use oxygen.

Additionally, carbon dioxide is one of the products of respiration and one of the inputs for photosynthesis. Carbon dioxide generally follows the reverse cycle for oxygen in our tanks. During the day the oxygen levels are higher and carbon dioxide lower and at night the oxygen is lower and the carbon dioxide is higher. Of course, the more circulation and surface area of water in contact with air, the less the deltas will be between night and day. Higher carbon dioxide levels are the reason that the pH may be lower in the morning than the afternoon.

 

[ATJ]

I have found a thick Kalkwasser paste to be very effective against Aiptasia.

[ May 26, 2001: Message edited by: ATJ ]

 

[Eric Borneman]

Right on Andrew.

As for if the powerhead was enough, who knows? Might have been, but only the O2 measurement would tell the tale. Fish are sensitive to it. As for the sponges, its possible, but I don't think you would have seen anything so sudden...slow clam demise if anything. Also, on the caustic soda is a troubling aspect.....for chemical as well as physical reasons...I wouldn't recommend using that...depsite its principle as competley dissociating in water, salt water reacts withit differently and forms globules in the water. If youa re going to use a strong acid or base for this, i'd use HCl and then buffer afterwards...safer and more effecive, IME>

eric

 

[Jim5]

Tehlia,

Since the main change was the skimmer and there was a quick demise, I would wonder about some type of poison. Was the skimmate somehow reentering the tank? Also, was the skimmer turned on again before the loss? I believe H2S can build up in this situation and cause sudden death when turning the pump back on. Maybe there was something on the new impeller?

Jim

 

[Mermade]

Thanks to all for your advise.
Jim, I was also wondering if the skimmate was reentering the tank. That's one of the reasons I turned it off before going to bed as the pump was blowing the bottom of the collection cup causing a mass of bubbles to the surface of the water. I didn't turn the skimmer on after the death until I fully cleaned it. I also cleaned the pump and have not changed the the pump over. I still think it is an oxygen theory but who knows.
Andrew, thanks for the insightful reply.
Tehlia.