I had a 10 gallon tank for about 40 days now. I was able to find a used 36 gallon tank. I have moved the gravel and decor from 10 to 36. In my 10 gallon two yellow mollies had white spots, I treated it using rid-attack (natural one). now one of the yellow mollies tail has black lines the white spots are mostly gone.

can i use the filter from the old tank in the new tank for a few days or will that spread any disease to the new tank.

I just moved one red molley from old to new and he is hidding behind trees since last night, does not move much. is he taking his time to settle down or something else

the 36 gallon bow front is very tall, when i put some food, not sure if the fish will even notice it. how will the fishes now i have put food. in a 10 gallon its very easy for them to find the flakes as they are falling right in front of their eyes

For the ich treat with salt and higher temps-- 1 tsp salt/ 5 gal, temps around 86*. I'm not sure what the black lines are though.

The fish will smell the food, don't worry.

and yes, you can use the old filter

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"Being ignorant is not so much a Shame, as being unwilling to learn".-- Benjamin Franklin

Your fish just may be a little stressed from the move. Keep an eye on it. Congrats on the new tank.