Willy Wombat Posted January 14, 2004 Share Posted January 14, 2004 Hi guys - I was just reading through another post being run on this page at the moment concerning the effect that heat has had on a few peoples tanks. Ie causing deaths to your little "preciouses". I just wanted to draw your attention to a few things that might help you understand why this is occuring. Hopefully i dont get too technical - but if i do please let me know and i will try and clarrify. So we all understand that oxygen is dissolved into the water from the oxygen in the air we breath. And we should also know that fish use up this oxygen and it needs to be replaced. This is why if you were to put a fish into a glass jar full of water and screwed on the lid - it would survive for a while, but eventually would die because it wasnt getting enough oxygen (it used it all up). So the oxygen goes from the air into the water through "diffusion" at the surface of the water in your tank. One thing that you may not realise is that water can only hold a specific amount of oxygen at any one time, and that a number of factors have an effect on how much oxygen can be in water at any one time. Temperature is a big factor along with the altitude you keep your tank at. The amount of oxygen in the atmosphere, decreases as you go up (ie breathing difficulties faced by mountain climbers), at about 4% less oxygen per 300 meters altitude. Less oxygen in the atmosphere equals slower diffusion with the water. Although i am going to leave out any more info on altitude, because it is not as big a factor as temperature, and Australia doesnt have very tall mountains!! The amount of salt in the water does have a small effect - but it is negligable at the concentrations used for keeping cichlids. Given that we are keeping tropical fish - Temperature has a bad effect on water. The hotter the water gets - the less amount of dissolved oxygen it can "hold". For example - water at 25oC can only hold about 80% as much oxygen as water at 15oC. 30oC would only carry about 70%! So if your tanks start heating up - then your fish are going to have less oxygen available in the water. Increased heat is also going to speed up metabolism and cause greater stress to your fish. Also consider at certain high temperatures, a negative effect will also be placed on some of the other biological functions of the fish too. Lack of oxygen may only be a partial cause of death at high temperatures (although it is pretty big) but there will be critical temperatures where fish will just die for other reasons, no matter how much oxygen they get! Someone also mentioned that their tank was dirty when they lost fish at high temps, and that this may have had an effect on the fish. It would most certainly had an effect! Consider this - microorganisms such as bacteria are responsible for decomposing organic waste. When organic matter such as dead plants, uneaten food, dead fish, and fish waste are present in water, the bacteria will begin the process of breaking down this waste. When this happens, some of the dissolved oxygen is consumed by aerobic bacteria, taking it away from aquatic organisms. This is refered to as the Biological Oxygen Demand (BOD) in your tank. To overcome it - you can either clean your tank to remove the organic load and reduce the amount of bacteria - or add extra sources of air diffusion (like extra airstones) to replace the oxygen that is being removed at a faster rate. Please be aware that the bacteria do not differentiate between night and day, and that the air must be supplied both night and day! Also - reducing the amount of fish in your tank will also make more oxygen available for obvious reasons. Anyway - hope this helped. WW Link to comment Share on other sites More sharing options...
23Skidoo Posted January 14, 2004 Share Posted January 14, 2004 To add to this i've found plants to be essential in maintaining oxygen levels in my tanks, with some cichlids this means planting your sump, my friend removed roughly half of the media in a 50L sump (an old 2' tank) and replaced it with a thick bed of elodea growing in a soil substrate. The inflow to the sump now flows through the planted section, under a divider and in to about 20L of bio-balls, then back into the tank. Water clarity is twice what it was, and over the summer he's had no fish problems. In one of my tanks without a sump i've made a cage out of plastic mesh about the same gauge as gutter-guard, it on-top of a ceramic pot of soil and gravel in which i grow as many plants as possible. The mesh stops the C Americans from destroying the plants but lets any fry through to safety. The essential part of both of these options is USE SOIL for your plants, add a layer of gravel to the surface to keep the soil from clouding the water. but it will make your plants grow stronger and better than ever. Your fish will thank you! Link to comment Share on other sites More sharing options...
Adam Posted January 14, 2004 Share Posted January 14, 2004 Skiddo, You've only got half the story with the plants. Plants do produce oxygen through photosynthsis. This only occurs when they have light. During darkness the photosynthetic pathway also ensures that plants use oxygen. So if you were to look at oxygen transfer to water and oxygen use they differ from night to day. Day Time Oxygen transfer - atmosphere, plants Oxygen Use - organisms (fish, bacteria etc), chemcial oxygen demand Night Time Oxygen Transfer - atmosphere Oxygen use - organisms (including plants), chemcial oxygen demand Therefore if your having problems in your tank the balance will be out. Adam Link to comment Share on other sites More sharing options...
Willy Wombat Posted January 14, 2004 Author Share Posted January 14, 2004 That is right Adam... Plants use up oxygen at night, which is why in aquaculture farms that have lots of algae - they use the most heavy aeration at about 4am in the morning, just before the sun comes up. All the micro algae in a tank use up oxygen at night too! Link to comment Share on other sites More sharing options...
Willy Wombat Posted January 14, 2004 Author Share Posted January 14, 2004 PS: did anyone find this post usefull? Or was it too technical. Appreciate your views so i will know for next time. WW Link to comment Share on other sites More sharing options...
fiona Posted January 15, 2004 Share Posted January 15, 2004 Not too technical. Aren't most fish people geeks anyway? Plants: 24/7: Respire (all living organisms, except maybe viruses (Dave?) respire). This uses oxygen and releases CO2. When light available: photosynthesise. This uses CO2 and releases oxygen - more than respiration releases/uses so in lit conditions the net balance is +ve for oxygen and -ve for CO2. You could light a planted sump ... Aren't most planted sumps used for nitrate removal rather than oxygen anyway? And lit in the dark hours (assuming perhaps that there are plants in the main tank? It's been a while since I read up on this). Link to comment Share on other sites More sharing options...
anchar Posted January 15, 2004 Share Posted January 15, 2004 Hi Willy, I found it easy to read - but then one would hope so after 7 years of tertiary study!!!. I don't know how technical it was for some of the younger/less experienced fish keepers though. Good point about the algae. People often forget that they deplete the system of 02 as well. merjo Link to comment Share on other sites More sharing options...
wazza Posted January 15, 2004 Share Posted January 15, 2004 Thanks for that WW a good read and good advice, ill go check the temps on my tanks right now! Link to comment Share on other sites More sharing options...
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