since my oscar died due to high nitrate levels which i have now got sorted out other fish that i have put into the aquarium all seem to die over night i have since seen my plec swim to the top of the tank like he is going for air would this suggest that there is a low amount of oxygen

oscarruss:

Nitrates are a problem easily solved by partial water changes.


Is your tank fully cycled? what size/volume of tank(s) do you have? What filtration system(s) -type and flow rate- are you using?

You can increase levels of dissolved oxygen by increasing water surface agitation -e.g. lowering a bit the volume of the tank so the output of your filter splash the water surface harder; adding airstones or bubble-wall assemblies; lowering a bit the tank temperature, and avoiding overstocking.

The combination of fish dying and gasping for air at surface suggest ammonia or nitrite poisoning to me. I would do as huge as possible water changer without disturbing your filter media; as for the substrate just remove any visible solid waste -uneaten food, fish pooh- but don't disturb it too much since your beneficial bacteria lives there too.

Please read around the articles in this site, and make yourself at home.

Pepe
Santo Domingo

the tank is a fluval duo 100 its 136 litres i'm using a eheim 2234 external filter its about 3-4 months old now. There is no trace of nitrites and only a small amount of amonia present in the tank i have got air stones and a diffuser on the end of my filter outlet pipe but i was wondering if perhaps there isn't enough aggetation in the water so was thinking of adding a power head?

I dont think think lack of oxygen is your problem as your will have to be very overstocked for this to kill them over night. As pepe says most likely are.
1 chlorine from untreated tap water. All tap water needs to be treated with de chlorine treatment.
2 ammonia as your tank isnt cycled properly
3 nitrites same issues as above.
4 you are shocking the fish by dropping them into differant water temputers. float new fish with bag open for 30 mins or longer in your tank before you release them.
The first 3 are my feelings where you are going wrong. to cycle a tank can take as long as 6 wks in some cases, and you shouldnt have fish in the tank while the cycle takes place unless you have keeped fish for some time and know how to deal with the problem that this will involve. Lastly what type of fish are you adding and I take it you have a heater.??

This size tank isnt large enough for a oscar.

we already have a plec 12" a clown loach 3" and a pictus catfish 5" we added 5 neon tetras which all died over night we then left it for 2 weeks and added 2 emperor tetras which again died over night

i am not sure but i feel aside from too small, your tank
is not yet fully cycled. i was made to believe that plec
is a very sturdy and survivor fish. if it died too, then
you have a big problem with your water.

the plec is fine the clown loach is fine which i thought would of died as they are a sensitive fish. I have no idea whats happening

could you post your water reading, ammonia, nitrites, nitrates, ph and temp. these might help in figuring out what could be wrong in your tank. also dont just say there fine as one persons definition of "fine" might not have the same meaning to another.

the amonia level is 0.6 nitrite was completely clear nitrates was 10 PH 8.2 and the temp is 26 degrees celsius 79 F

you have answered your own problem. An ammonia reading of 0.6 is around middle of the scale(just under). if you put a stressed (new) fish into these surroundings it will have problems. when you buy a new fish it will be stressed, stress makes the fish produce more ammonia in the gills than normal. With a high level of ammonia already in your tank it dose not have much chance. your tank should have 0% ammonia. your tank is not cycled or you have damaged your cycle cleaning your filter. there is also the possibility your filter is not up to the job or is not working properly.(i can't remember what filter you have,I will go back and look in a minute) A nitrate reading of 10pph is very good and i am surprised its this low. this leads me to think you have just done a major clean or water change and because the cycle is lost no nitrites,nitrates are being produced. your PH is high too but this is most likly to do with your current problems. we can look at these when the first and most important is sorted.

I would recommend you do a 50% water change ASAP, followed by 30% water changes every 2 days after. monitor your ammonia & nitrites an till these read 0%. Heat your water change to same as your tank.DO NOT ADD MORE FISH YET.when your readings are 0% check your ph. a stable PH is more important so dont try to adjust.

Ok i just checked your filter it good for 44 gallons so is just about right for your tank size of 35ish gallons. Its best to have much more filteration than your tank. can you tell us about how you clean and maintain your tank and filter, how often you clean your filter.how often you do water changes.you say its a few months old have you cleaned it in this time. last what media do you have in it.

i have cleaned the filter media twice in this time by rinsing it with the tank water (do i have to tip the water that is in the filter away)i clean the water in the tank once aweek about 25% water change then replace the water with fresh water and add aquasafe. The media in my filter: blue course sponge at the bottom bio balls in the middle a filter pad and carbon pad at the top

twice in 4 months isnt far off so i dont think you are over doing it.your water change is about right two. the only advice I would add is-

when you do a water change, if you like most people add aquasafe then new water,(aquasafe gose in before new water)you should turn your filter off say for 10 mins so aquasafe can work. while its off move water around inside tank by hand. This is to make sure no chlorine gets into your filter. if you add aquasafe to new water before you put it into your tank you dont need to turn filter off. as for emtying water from filter,sometime i do if its very dirty in bottom but most of time I dont. only clean one third of your media at a time. never wash both sponge and media ball at same time. if you open filter say after 2 months and its clogged and very dirty,open earlier say a month but only wash one stack.

hopfully if you follow the above, your ammonia will go within a wk or two. your main goal is to remove ammonia & nitrites once this is done your wkly water changes will keep the nitrates down.