Hi there
i agree with the others,its not normally the filter that kills fish,i have two externals on my tank,which have quite a flow rate and even the fry can swim around the flow etc.
What are your water stats for ammonia/nitrite?
reading a previous thread of yours you say you have goldfish in your 50 gals,are these in the same tank? Goldfish are big waste producers and this may affect your water quality and your water stats
Has your filter been cycled?
Basically, this is what I did... I got my aquarium set up. I put a tropical fish flake or two in the water. Obviously, without fish, it didn't get eaten. It only produced ammonia. The filter ran for 24 hours, after I put that one flake in the water to produce the ammonia. I then bought three comet goldfish. After adjusting them to the water and all, I obviously put them into the fifty gallon tank. Anytime the fish are around the filter, I've noticed that they (most of the time) swim down and vertically; never straight. One of the fish I have swims around the filter freely. Never got sucked in or up against it, but I have seen it struggle from time to time to swim freely away from it. The other two fish however have got sucked into the filter. By the time I noticed the first one get sucked into it or up against it, it was too late. It was already dead. I saved that one once before, because this happened twice to that same fish; it died the second time. The other one got sucked into it once, but I noticed it on time and rescued it from the filter suction. Hasn't happened since. However, the fish are almost always on the opposite side. It was cycling a fish-in cycle with two fish in it and many plants. I figured since it's such a large tank, with such large room, and such a small amount of small fish, it'll cycle slowly and productively with little to no harm to the fish.
I had a ten gallon before I had this fifty gallon. But I got this fifty gallon pretty cheap at a yard sale, and decided to take it. Who wouldn't, right? But the filter and equipment that came with it didn't come with the packaging and such. The filter that I have says "Aqua-Clear 70" along the top.
I just want to know what's going on with the filter, why it's murdering or attempting to murder my fish, and how I can prevent this? I want to use my fifty gallon for smaller fish, such as tetras for instance, but I want a filter that I won't have to worry about at the same time.
Hope this information helps. Sorry about being so vague before, (I was at Wal-Mart viewing filters and my girlfriend was on this account for me typing this up and telling me the info over the phone to help me with information I may have needed.) Hope this is a bit more detailed now, though. I appreciate the help from everyone. Thank you all so far, and thanks again to those in advance!