Hi and welcome to the site.
Whilst I agree with much of what has been said, I will add my slant on this (and it may be controversial to some).
I don't know how much you know so am gonna ask some questions, please don't be offended if they seem basic.
Firstly, I would like to know about your filter - size, type, internal/external, set up as bought from shop or modified. etc.
Also, what you are calling bio media. these will be the ceramic bits of tubes for example and are not the foam pads (they are mechanical (generally). Some filters don't have bio bits and only have the mechanical bits which in turn are expected to do both rolls. When you clean either then it's a case of washing in tank water, not replacing altogether and not washing under the tap.
The foam pads should reside at the inlet (generally bottom of a filter) to prevent the bio bits ( often at the top or outlet of the filter) from getting clogged up.
1 gulper cat in 40 g to me does not sound bad to start with as they are fairly sedentary but they can get to 12" so you may need to be looking at a slightly bigger tank soon. More also that gallons are different US to UK and I dont see your location.
I have been keeping fish over 40 years and know very few aquarists that religiously change 50% of tank water weekly or more. Some fish don't like such water changes and sometimes based on tank/pond volumes it's just not practical. Personally I do 10 to 20% per week. Even our fish keeping magazine (that has been around almost as long as me) only recommends 20-25% weekly.
the important thing is to get your water stable and decent, nitrates 40 or under would be good - obviously the lower the better, but you may find it comes out of the tap or the ground already reading 40!!!!I
As for ph, I would suggest that without some kind of buffer (crushed coral for example) your ph will drop over time and this can in some cases get as low as 5. The best way to either bring it back up or to keep it stable at 7 is to add some of this crushed coral. if you do want to change the ph via a bought product, please follow the instructions, as ph changed should be done over days or even weeks.
Not sure the choice of fish is a bad one as a first fish. Certainly interesting but I can see why it was chosen. There are certainly harder fish to keep and even fish like guppies, dwarf gourami, or other so called community fish would have been worse choices.
I don't know the vitamins in frozen silver side but you may look at varying it's diet from just these to other types, although many fish get used to eating one thing and one thing only so vitamin supplements may be a good idea (again, never used them personally).
get the water good, let him fast a little and hopefully he should be back to normal soon!
Whilst I agree with much of what has been said, I will add my slant on this (and it may be controversial to some).
I don't know how much you know so am gonna ask some questions, please don't be offended if they seem basic.
Firstly, I would like to know about your filter - size, type, internal/external, set up as bought from shop or modified. etc.
Also, what you are calling bio media. these will be the ceramic bits of tubes for example and are not the foam pads (they are mechanical (generally). Some filters don't have bio bits and only have the mechanical bits which in turn are expected to do both rolls. When you clean either then it's a case of washing in tank water, not replacing altogether and not washing under the tap.
The foam pads should reside at the inlet (generally bottom of a filter) to prevent the bio bits ( often at the top or outlet of the filter) from getting clogged up.
1 gulper cat in 40 g to me does not sound bad to start with as they are fairly sedentary but they can get to 12" so you may need to be looking at a slightly bigger tank soon. More also that gallons are different US to UK and I dont see your location.
I have been keeping fish over 40 years and know very few aquarists that religiously change 50% of tank water weekly or more. Some fish don't like such water changes and sometimes based on tank/pond volumes it's just not practical. Personally I do 10 to 20% per week. Even our fish keeping magazine (that has been around almost as long as me) only recommends 20-25% weekly.
the important thing is to get your water stable and decent, nitrates 40 or under would be good - obviously the lower the better, but you may find it comes out of the tap or the ground already reading 40!!!!I
As for ph, I would suggest that without some kind of buffer (crushed coral for example) your ph will drop over time and this can in some cases get as low as 5. The best way to either bring it back up or to keep it stable at 7 is to add some of this crushed coral. if you do want to change the ph via a bought product, please follow the instructions, as ph changed should be done over days or even weeks.
Not sure the choice of fish is a bad one as a first fish. Certainly interesting but I can see why it was chosen. There are certainly harder fish to keep and even fish like guppies, dwarf gourami, or other so called community fish would have been worse choices.
I don't know the vitamins in frozen silver side but you may look at varying it's diet from just these to other types, although many fish get used to eating one thing and one thing only so vitamin supplements may be a good idea (again, never used them personally).
get the water good, let him fast a little and hopefully he should be back to normal soon!
