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CO2 wiped my tank overnight

Wooly1970

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Hi all. Sorry for the lengthy post, I just wanted to give as much background as possible to my query.
I was hoping for some insight and advice on what went wrong with my recently installed CO2 system. I went back to the aquarium specialists that I bought the system from, but I think they were grasping at straws for what killed.my fish overnight. I have been running my 400 litre tank for a couple of years without too many water issues but have never been able to keep plants alive. Yesterday, I bought and installed and expensive PH controlled CO2 system which runs in line with my enhiem cartridge filter. My water stared with a PH of 7, a KH of 40, no noticeable ammonia and a NP2 of just over 0. I set the CO system to target a PH of 6.7. It got down to the target PH fairly quickly and maintained it for the next few hours before the lights switched off. The CO2 indicator bulb by then was a nice green, fish seemed happy and I went to bed feeling happy with myself. Unfortunately this morning when I first checked the tank (some 12 hours later) all of my fish bar 2 loach eels and a bristle nose catfish were dead. I re-read the water and the PH was 6.67 NO2 was 1 (possibly because I had 20 plus dead fish floating in the tank overnigh), no noticeable ammonia and the KH was 80 (which could be an anomaly with the test strips as it tested and 80 a few hours after the sample was removed from the tank). The aquarium shop after much umming and arrring finally came back to me proudly saying that they had found the issue to be the nitrates. My nitrates (NO3) are high and have always been high (140). I have always been told that the nitrates will have little affect on the fish and I can attest that fish have always been happy and healthy until I started the CO2 system. Is there some truth in the combination of NO3 and CO2 being the single cause of a almost 100% fish kill overnight or should I look elsewhere?
 

Byron

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Welcome to TFF. There are a couple of important factors here.

First, you do not need diffused CO2 to grow aquarium plants. The issue with your plants was either light or basic nutrients or both. I do not know the light data, nor the nutrient situation (fish load/feeding, water changes, parameters (GH especially), added plant supplements), and the plant species and numbers, si I cannot offer any suggestions, but this is something we can go into later.

Second, was the CO2 running at night? If yes, undoubtedly this killed the fish. CO2 if used can only run during the day when the plants can use the CO2 (provided the light is of sufficient intensity and spectrum and all necessary nutrients are available). At night, CO2 builds up and can easily kill fish. This is sometimes an issue even in planted tanks without added CO2, as the CO2 from the normal respiration of fish, plants and some bacteria can build up during darkness. I have seen this in my own tanks, and easily solved it by increasing the surface disturbance from the filter return as this increases the CO2 and Oxygen exchange.

Third, nitrates at 140 ppm are way too high for any fish. This may not kill them outright, but it does seriously weaken them which makes them much more susceptible to other issues that they would normally be able to deal with, but cannot because of the weakening from high nitrate. Nitrate in a fish tank should never be above 20 ppm, and it shoould be lower, as low as possible. Ammonia, nitrite and nitrate are all toxic to fish; in the case of nitrate, fish are being detrimentally affected buyt the effect depends uppon the level, the exposure time, and the species.

Unless you want an aquatic garden with no fish, I would forget CO2 and return the unit. I would be happy to offer advice on having a successful planted tank where the fish will be healthy. I've had these for nearly 30 years now without adding any form of CO2 beyond what naturally occurs.
 

Retired Viking

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Sorry about your fish, this is a good place to learn so you do not make the same mistakes again. I have also made plenty of mistakes over the years and lost fish. I have two planted tanks the do just fine without CO2. Don't give up, learn from your mistakes and try again.
 

Stan510

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I just saw a George Farmer vid of a large planted tank with no Co2...and there they were thriving...Trident ferns,Hygrophila pinnatifida and many species of crypts.
I know Co2 would make plants grow faster...but that push usually means you have to keep a very light fish load. I think if you had tried iron ...at the very least it would have greened up the plants along with making sure you had the right lighting.
Good luck.
 

Byron

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Are these Co 2 pumps supposed to come with timers then?
I've never used diffused CO2 but from what others have posted here and on the plant forums I gather most have the CO2 regulator on a timer with the tank lights, so the CO2 is on when the light is on and off the same. In addition, many of these folks also run an additional filter (or somehow adjust the regular one) to provide much more water surface disturbance during the night to encourage the exchange of oxygen and CO2 at the surface; oxygen enters the water and CO2 dissipates out.
 
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Wooly1970

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Update. Firstly, thank you to all for your input and advice.

I have just had a visit from a vet that specialise in fish and aquariums. The prognosis was - water quality was and remains in the good range, PH 7 gh 40, nitrites well in range less than .25, nitrates still high but as per his diagnosis will not have any effect on the fish unless well over 200. Bio filter is working very fast and the main reason for the high nitrates, which ironically will decrease as my plants mature and start using more of it. PH settings I had used for the PH controller were correct for my GH of 40.

So what killed the fish? In his opinion it was a combination of the bad advice to run the CO2 even with the PH controller, the increase of CO2 manufactured by the plants overnight and a possible fault with the PH probe which was observed during his inspection.

The Dr's advice was the CO2 is to go off 1 hour befor lights out and 1 hour after lights on. The air curtin is to run when lights are out only. (This is pretty much the same advice that I have received since my sad incident and should have been the advice that the supplier gave me)
 

essjay

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Plants respire the same as animals do. They use oxygen and food and turn them into carbon dioxide and water. They do this 24/7.

When it is light, plants take in carbon dioxide and convert it into food and oxygen, a process called photosynthesis. Plants cannot photosynthesise when it is dark.

During the day photosynthesis is greater than respiration, so there is an overall increase in oxygen and an overall reduction on carbon dioxide. But at night, plants only respire, so oxygen is taken up and carbon dioxide released. And of course the fish are respiring as well, further depleting oxygen.
Gas exchange occurs at the surface 24/7, and running an airstone at night increases gas exchange so the fish don't normally suffocate. But if carbon dioxide is pumped into the tank at night, there is more carbon dioxide than gas exchange can remove so it builds up and suffocates the fish.
 

Byron

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Essjay nailed it bang on. Fish, plants, and many (but not all) species of bacteria respirate the same, using oxygen and expelling CO2, and this continues 24/7.

The advice on nitrate in post #8 needs correcting. Nitrate is poisonous to all fish, period. It simply differs from ammonia and nitrite by having a less intense or less obvious or less detrimental immediate effect--i.e., the fish do not turn belly-up and die like they would with very high ammonia or high nitrite--but the fish are still being affected negatively. The higher the level of nitrate and/or the longer the fish are exposed to it, the more damage it does to the fish. It will in time kill them.

As Neale Monks explained this to me, the effect of nitrate most often is a general weakening of the fish. This is the same as the effect of stress; the fish has more difficulty performing normal biological functions and as this continues the problem becomes more and more debilitating until the fish can no longer manage, and it dies. Often the death occurs sooner as the result of some other issue; the weakening of the fish impacts the ability of the immune system to function so the fish will be more susceptible to disease, bacteria, etc, and eventually unable to effectively fight it off. The highest level nitrate should ever be is 20 ppm. And this level will seriously impact some fish--including cichlids. Over on the cichlid site there is evidence that nitrate is likely as responsible for Malawi bloat as diet. Of course, the two may be connected--the nitrate impacts the fish's system and nutrition may be affected.

Nitrate should always be kept as low as possible, and never above 20 ppm. This is one problem with high-tech planted tanks that dose nitrate--fish present will be affected.
 

snailaquarium

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when plants get light, they photosynthesise and use carbon dioxide (CO2) and release oxygen (O2) as a byproduct.

at night when it's dark, plants use oxygen and release carbon dioxide.
Does the same happen with trees?
 

Deanasue

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Essjay nailed it bang on. Fish, plants, and many (but not all) species of bacteria respirate the same, using oxygen and expelling CO2, and this continues 24/7.

The advice on nitrate in post #8 needs correcting. Nitrate is poisonous to all fish, period. It simply differs from ammonia and nitrite by having a less intense or less obvious or less detrimental immediate effect--i.e., the fish do not turn belly-up and die like they would with very high ammonia or high nitrite--but the fish are still being affected negatively. The higher the level of nitrate and/or the longer the fish are exposed to it, the more damage it does to the fish. It will in time kill them.

As Neale Monks explained this to me, the effect of nitrate most often is a general weakening of the fish. This is the same as the effect of stress; the fish has more difficulty performing normal biological functions and as this continues the problem becomes more and more debilitating until the fish can no longer manage, and it dies. Often the death occurs sooner as the result of some other issue; the weakening of the fish impacts the ability of the immune system to function so the fish will be more susceptible to disease, bacteria, etc, and eventually unable to effectively fight it off. The highest level nitrate should ever be is 20 ppm. And this level will seriously impact some fish--including cichlids. Over on the cichlid site there is evidence that nitrate is likely as responsible for Malawi bloat as diet. Of course, the two may be connected--the nitrate impacts the fish's system and nutrition may be affected.

Nitrate should always be kept as low as possible, and never above 20 ppm. This is one problem with high-tech planted tanks that dose nitrate--fish present will be affected.
I am quite perplexed by your vets guidelines for nitrates. 40ppm is the extreme and lower than20 ppm is the goal. Most shoot for 5 - 10ppm. Why are your nitrates so high?
 

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