Fish Dying Periodically? Filter Mod. Ok?

Hey everyone. Got two questions really bothering me :
1) why do my fish keep dying periodically? Usually takes around 3 weeks for the next fish to die. Be it guppies or dwarf gouramis. They just die out of nowhere. Have had the current stock for around 2 months. They eat like pigs and show no signs of illness except for an hour or so right before they die.
Have no water kit unfortunately so can't tell about the parameters. But it's only logical that if there was trouble with water quality,all fish would be effected . Right?
This brings me to the next question regarding filtration.
2) In the 90 gallon, I have 2 internal filters (800 gallon per hour flow) and diy sponge filter with biomedia in a large bottle that uses an air pump.
The internal filters I have , I modified them and took the sponges out and filled with biomedia ceramic rings. For mechanical filtration in the filters, I put socks over the intake slits which I clean weekly. This should work fine right ? Just want to make sure this method works and rule out that my first problem has anything to do with the filtration.
Below are the kind of internal filters I have. Not exactly these but basically the same design and stuff.

Thanks

 

 

most likely water conditions, possibly aggravated by stocking issues. what is your stocking? why are you cleaning the sock (let alone why are you using it) and how are you cleaning sock. No poor water will not necessarily kill all fish, some fish even of same species are hardier than others. also water may not be ideal so any additional stressors like bullying will cause fish to die.

 

One can't know what is happening with the water without testing it. A test kit like the API Master Freshwater test kit is less expensive in the long run than constantly replacing fish that are dying from poor water conditions. You may have perfect conditions in the tank but without testing we can't know.

How often are you doing water changes? How much water are you changing out each week? Is this tank cycled? Do you know what that means? Most of the time we can get to the bottom of the problem and most of the time it is caused by less than ideal water conditions.

 

It's best if you could find a way to test the water parameters...gives you a better idea of what's going on in the tank. Also not quite even if the water parameters are off some fish can withstand it better than others even those in the same species. Sometimes you get some fighters who can take the abuse for a bit before dying. (Let's hope this isn't the route we are taking). If the test kit is too expensive atm you could always try getting test strips they're a lot cheaper, but they aren't as reliable. But at least they'll give you an idea of what's going on.
Kind of curious as to why you are using a sock... easier to just use a sponge and a rubber band. Plus I think the sock might be frilling if it's been submerged/placed in/or is constantly wet. Which means it may be slowly coming apart and tiny bits could end up floating into the water and getting into the fishes causing them to choke or if swallowed blocking their intestines. Other than that it could be a number of things like parasites or bacteria. Though parasites tend to take time to kill fishes.