Clean the filter if it has one and check the check valves if you are using them.Tetra and most higher end brands can be rebuilt.Big Al's has the parts for the Tetras and maybe some others.
It's a 60-100 gal tetra pump. I checked the cotton filter and there were some black stuff on it. Other than that taking it out doesn't seem to make it any better
Goldfish ftw!!!
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080215 Yopoipoi, rest in peace. May the river of light guide your soul to the celestial waters above.