dirty water

Question
hi, we have two common goldfish and 1 algae eater. We bought these fish 7-8 months ago, as they grew bigger, we noticed the water was also getting more and more dirty or foggy to the point that you couldn't even see the fish. A few weeks back, I washed out the fish tank - 25 gallons- completely. The water was crystal clear for about a week but now it is back to foggy. What can I do to keep my water clean? i have a hanging filter and an undergravel filter. I change 20% of the water every week, i clean the overall tank after every 6 months.  

Answer
The biological balance has been disturbed and the nitrogen cycle has to get established again. Cloudiness is a common side effect. I never recommend a 100% change unless there has been serious illness, accidental toxins have been introduced or some other serious event. When you clean out a tank competely it kills the beneficial bacteria in the system that helps keep toxins controlled and the water clear. Changing the filter too often, overcrowding and overfeeding are major contributors to cloudiness as well. If a filter is "too clean", there isn't enough mature beneficial bacteria in the filters to keep the water clean. Toxins rise and cloudiness is the result. It basically has to "break-in" all over again and can take up to 8 weeks to re-establish the nitrogen cycle as if the tank was brand new.

Goldfish are very messy guys and it can be very difficult to keep their water clean. It is important not to overfeed them. Goldfish are mostly vegetarian and most of us feed them too much commercially prepared dried foods that are too high in protein and not enough fiber. Cut back on regular food by 50% and feed veggies in place of it. I give my goldfish slices of cucumber, squash, peeled cooked peas, cooked green beans, romaine lettuce, raw spinach, slightly cooked shredded carrots. Just rinse them and drop in the tank. It is safe to let them nibble on these for a day or more. Regular food must be removed within a few minutes if not eaten because it rots so quickly. Not so with veggies. When you feed regular food, make sure that you only put in enough that the fish consume all of it from all areas of the tank in less than 5 minutes. Feed once a day.

An undergravel filter is really not a good choice for messy goldfish. It would be best to remove it and get a second and/or larger hanging power filter instead. Goldfish waste is just too big and in too large a quantity for an undergravel filter to work properly. Cloudy water is very common when using undergravel filters with goldfish. Make the gravel very shallow, no more than an inch, so that wastes don't get trapped in it. Undergravels can only operate efficiently if oxygenated water flows freely through the gravel and bottom plates to keep the beneficial bacteria alive. Goldfish and other big messy guys' wastes just don't allow that to happen.

At Your Service;
Chris Robbins