My Goldfish are hiding

Question
QUESTION: My tank is 75 gallons. I have 14 goldfish, all over 5" in length, 2 Black Moors also very large, and 1 long fin Koi that is only 3". I also have 2 3-4" live mussels. 1 4" Placo. The tank has been well established for over a year. The water here is terribly chlorinated so we use strictly rain water or clear creek water. We keep the water at room temperature of about 70 degrees. This has worked fine the whole time. I have Rocks, big and small built into caves and sea shells  along the bottom. We do not use gravel because the fish tend to try to swallow it. I have already lost 1 because of the gravel, so now we use sea shells. The tank has been like this since I set it up a year ago. the water is crystal clear. The filter I have used since day one is from my old pond. It has 2 black inserts that we clean out every week and reuse. This filter lays at the bottom of the tank and circulates the water. There is an abalone shell lying across the top of the filter in such a way as to slow the current. I have an air pump putting bubbles into the water but have noticed recently that I have to keep fiddling with it to make it work. I am going to replace the pump. I think its has seen it's last days. the problem is that my fish, all of them are trying to hide under the same rock in the bottom corner of the tank. The eat normally, then go back to the rock. I do have a florescent light across the top of the tank that we leave on about 8-10 hours a day and have also done this since the beginning. We do a 50 -70% water change about once a month but for the most part we have beautiful tank. Have my fish gotten too big for their environment? My husband keeps hitting the side of the tank to get them to come out of hiding. He say's he is making them get some exercise. Are they now after all this time, scared? These fish are about 5 years old, my babies. Please Help. I am sorry that this is so long but I wanted you to have all the facts. Thank You, Melodie

ANSWER: Hi Melodie:  Your husband needs to get another hobby... hitting the tank causes great pain to your fish. They have an organ that senses vibrations and when someone hits the tank that organ flares and hurts them.  I would hide under a rock too.  Fish that hide are scared of something and everything that you have described in terms of the care of the fish is good except your husband.  Bubblers need to be replaced every so often because they tend to clog on the inside with debris which when air passes through the debris is pushed into the bubble stone... so when you take the air pressure off the debris falls and the bubbler works again for a bit but then begins to clog slowly.  Goldfish also need to have their water changed at least 20% weekly. They are very messy fish and their urine and poop will cause the water chemistry to become toxic.  dave

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QUESTION: Thank You So Much! I read my question and your response to my husband and needless to say, he isn't very happy with himself right now. I am going to get a new air system and restrict my husbands interaction with MY BABIES. I do change out about 15 gallons every week, is that enough? I am also a little concerned about the quantity of fish I have in my tank. They don't seem to be crowded but they have gotten really big. I do have a pond outside with a couple of little, 2-3" goldfish and a 4" bluegill. Is it safe to put a couple of my aquarium fish in the pond if needbe?

Answer
Hi Melodie:  Goldfish can grow to be quite large.  I have seen them around 20 inches including their tail.  They grow based on the size of their environment.  You can put them into the pond but you would have to acclimate them slowly to the pond conditions by mimicking them in your tank... temperature and pH being the bigger issues.  dave