Friends,

I need your help here...

This is the situation...

I have got to redo an Oscar tank set up.. its a 5 feet long tank with height 2 feet and width 1.5 feet.

This tank currently has stones as gravel.. this was orginially not meant for Oscars however, over last period of time, 5 Oscars have been living here happily ( all less than 2.5 inches in size as of now)... The reason I want to do this, is the gravel stones has lot of sharp edges and also it does not add any beauty to the tank...I am planning to replace this big gravel stones with Quartz gravel which is of much smaller in size and easy for me to take the muck out.
Currently all the muck gets trapped in between the large stones and while siphoning out I get hard time.

This tank has 2 internal power filters running in addition to an under gravel filter... The water is clean as I perform 10-15% of WC twice per week. The tank has cycled and is stable for last 3 months...

Now when I change the Gravel/substrate, I realize I would be loosing a large bed of beneficial bacteria..

Now how do I proceed so that i force a fastest nitrogen cycle or minimum impact on the tank inmates...

This is what I thought of.

1. This time I would be siphoning out water from the top (taking out the aged water existing in the tank) in a clean bucket and would then net out the Oscars...
2. about 60 - 70%% of the water I would use would be existing water from the tank..

3. Then I would take out the Gravel, which would obviously make the entire left over water dirty. That water I am afraid, I may have to throw out after the cleaning the bottom completely...

4. Arrange the new gravel below (which would be kept washed already)..

5.Pour the Oscars with the water in the tank,

6. Use the remaining portion to be filled with clean water.

In the whole process, I would not be touching the power filter media.. which means the filter medium would not be cleaned at all..


Is this right, or I am going wrong somewhere....
I want to do this, but somehow not getting the confidence.. I definitely do not want to have a disaster

even though some beneficial bacteria lives in the substrate of your tank the majority is housed in your filters. your plan for changing your substrate sound good to me the only i would change i would do is to add the new water(at the same temp as the water the oscar are in)then add the remaining water with the oscars. try to accomplish this as quickly as possible and keep the biological media in your filters wet and you should have no adverse side effects.
make sure to take water readings for a few days after you change the substrate to make sure you dont get an ammonia spike.

OKK BOSS...
Got it... yeah I forgot about the temperature part.. Planning to do this exercise this weekend.. would keep you posted... meanwhile let's see if OFL adds any more piece which I may have missed

Seems like you got a good idea on what your doing. Only thing I would add is turn off or make sure your heater stays in water or it may crack,(dont put hot heater in cold water) heat new water as necro says and if you are putting new water straight back into tank turn pumps off for a short time so they dont come into contact with untreated chlorine, Its best to treat your new water before you put it back but most people dont do this.

I had to do this once when i wanted to put a UGF in. I took out all the decor, scooped out most of the gravel, syphoned the last few bit outs, put the UGF in and then put the gravel in. I then did a 50% water change. I did this with the fish in the tank. Fish were not too happy and the tank got a bit murky but things soon settled down.