What have I done??

Question
Hello, I have 4 goldfish and a tiny catfish in a 35 gallon tank.  The oldest fish is 8 years and the others are all 4 years old.  I scrubbed algae that had accumulated on the tank walls the other day, and then started to spray off the filter media every couple of hours to get the water to clear up.  I've done this several times before, but this time, I used a sponge from the grocery store.  The sponges are not the kind with soap in them, but I think they must have had something anyway.  I noticed last night that the fish appeared "tired" so we checked the water.  The nitrates were fine, pH was low, no chlorine, etc.  I did a 1/3 water change and scrubbed at their tank a little more.  Today, all four fish look "tired" and I've noticed that they seem like they can't see.  The are running into the side of the tank quite often- I don't know if that is because the walls aren't covered with algae or if something is wrong.  I don't see any indications of ick or anything like that- just tired, droopy fish that don't want to eat.  Two of them are also shaking their heads every so often.  I did a 1/4 water change tonight but I'm afraid of changing the water too often and stressing them. These are super hardy fish- they've dealt with the tank getting way too hot and then having me throw ice in it to cool it off, they've been fine with a variety of things (plant leafs, spiders, etc.) that have fallen in the tank.  I change their water infrequently, but we check for nitrates, pH, chlorine, etc. frequently to make sure that we don't need to do anything else.

Answer
Hi Jami
Well, not sure really what's going on.  Usually when a fish is "poisoned" by something in the water or added to the water, they'll swim and dart around the tank like mad.  What I"d recommend doing at this point, pick up a test kit for ammonia and also nitrites.  Those are probably more important then the other tests you have.  You want to make sure the ammonia and nitrite are both reading 0 ppm.  Nitrates you want to keep under 20 ppm.  What's the ph reading, you said it was low?  Also monitor that, is that fluctuating or is it staying stable?  IF the ph is fluctuating, that can stress them and cause them to act the way they are.  So could ammonia or nitrite poisoning.

You said you sprayed off the filter media, what do you mean by that?   Did you put it in the sink and rinse it off?  IF so, not a good idea if you're on a public water supply that uses chlorine or chloramines, because that will kill off your beneficial bacteria that's growing in there-causing ammonia and/or nitrites to start showing up.  The sponge, to be on the safe side, don't use that.  Get an algae scrapper/pad from the pet store that's made for fish tanks.  That way you know it doesn't have any chemicals in it.

Get those other test kits, and let me know what the readings are, as well as the ph and if the ph is staying normal or fluctuating around.  Also, it's a good idea to get into the habit of weekly water changes of 25% along with a weekly gravel vacuum.  I only recommend cleaning off the filter pad in a bucket of used tank water maybe once a month, and only changing the filter pad about every 3 months.

CHristy