Fixing Cloudy Freshwater Aquarium
A fish tank with crystal clear water and nice make-up is pleasing to the eyes and gives a pleasant feeling. If you think there is still something to improve, do it. It is OK to be a perfectionist here. Do not settle with a less desirable tank.Your bio-filtration system should have bigger filtering capacity than your tank volume. If there is still enough space, use two filters.

Cloudiness may not mean the water quality is not good for fish. It may be more to just an appearance problem as it kind of defeats the decoration purpose of keeping fish tank in the living room. Two areas of cloudiness:
a) water
b) internal wall of tank (you can see the murkiness clearly under the aquarium light in dark surrounding)

To clean internal surface of tank, simply use a sponge to rub the internal wall. No need to evacuate the fish. Rub the internal wall from being slimy to being squeaky. The aquarium light should be turned on so that you can see which area is still murky.

After major turnover cleaning in which everything is cleared from the tank and is washed thoroughly. 100% water change, every tank is considered new and new tank syndrome will happen. Not only the water in the new tank has more tendency to become cloudy (due to the lack of beneficial bacteria) but also some fish may die. Do not do 100% cleaning.

If it is an old tank but there is no bacterial / biological filter, the beneficial bacteria has no place to colonize so they swim all around and the water looks cloudy.

Even if the tank has a filter and water change is done everyday, the water may still become cloudy. Reason:
a) Too many fish in a small tank.
b) Too much excretion or leftover food due to overfeeding. By the way if it is due to leftover food, the cloudiness is usually whitish.
c) Not enough oxygen for beneficial bacteria.

What you can do for the water:
a) Produce more bubbles so that more oxygen dissolves in water for beneficial bacteria to break down fish excretion. Of course first there must be media for colonization.
b) Change more water more frequently (e.g. from a scoop per day to a bigger scoop).
c) Wash filter floss more frequently. Wash the filter pad in the water that is scooped out of the tank, not tap water to preserve the beneficial bacteria.
d) Add in a few more plants (Egeria densa, Java Lace Fern or Anubias). Leave enough space for the fish to swim though.

If those do not work even after a week, put activated carbon pack in the filter. If it still does not work, it may be due to some microorganisms. Some salt can be put in to kill them. If it fails again, take out a few fish that you think less attractive, increase the size of the power filter (if it is not the biggest yet) or add another power filter. The final way is to have a tank cleaning without moving out the things and fish. Clean the plant too if dirt is trapped by the leaves. Then use a pipe to siphon out the dirt at the bottom. Leave some water in the tank enough for the fish to breathe while you go pour way the dirty water and prepare new water. After this major change of water, the water may still look cloudy but it is alright. The water will become clear after one to three days depending on the availability and the size of beneficial bacteria colony in your filter.

I mention about how I change water in Freshwater Aquarium Fish Survival.
Posted: 2007-01-31; updated: 2011-04-26 by Ong Seng Aun.
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