I set up my first tank (50 liters cube) about 4 days ago. It's quite high-tech:

  • CO2 injector
  • Macro + Micro fertilizers
  • 6h / day lightning
  • I added some aquarium starter fluid
  • Decent filter with a bunch of ceramic rings (not colonized by bacteria yet)

There are no animals in this tank, plants only. The water is not really crystal clear - it's a little milky.

I noticed some whitish goo forming on the gravel and driftwood (see the photos below - what looks like cloudy glass is actually this goo growing on gravel). This goo is quite solid, it waves.

What is it exactly? Algae? Fungi? Should I care and take some action or should I just wait for it to pass?

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3 Answers 3


Your tank is not properly cycled yet. Take this a bit slower, do not add any animals to your tank until it is properly cycled.

The gray you can see in your tank is bacteria starting to grow. It is normal to have this in the beginning before the tank is in biological balance.

The gray stuff will go away after a few days and it is not only bacteria, but several types of living things that you can find in a healthy tank.

You need to get a water test and measure the level of ammonia. Finding ammonia in the water is the first step when you cycle the tank.

After a few days you will be able to measure nitrite and ammonia in the water, nitrite level will go up and ammonia level will start to go down slowly.

After a few days, all of the ammonia will be gone and the level of nitrite will slowly fall to zero.

After all this is done, you will only be able to measure nitrate in the water - this is the end result of a healthy biological prosess; the nitrate is plant food.

You can take a look at this article on fishlore.com to get more and better information about how to cycle a tank.

Do not add any animals to your tank until it is fully cycled.


You did too many things in too little time. Maybe you want to take a step back and do things gradually. In that way, you will be able to better understand the source of your problems.

  1. Move everything is a different vessel(s) (can even be larger glass jars).
  2. Properly clean and disinfect the aquarium (gravel, filter, other accessories also); be sure to remove any traces of chemicals, they have the ability to ruin all next efforts.
  3. Add the gravel, the plants and the light; also add the mechanical filter; no CO2 or fertilizers at the beginning.
  4. Assuming that "aquarium starter fluid" is actually beneficial bacteria, add that too.
  5. Monitor the progress, adjust as needed.
  6. Add fertilizers only if the plants are sad, and only in very small amounts.
  7. Add the CO2 when things are mostly stable, and only if needed; if the plants are well without it, do not bother.

As already answered by @SimplyRedAppaloosa, be sure to properly clean everything else which goes into the aquarium. You might want to add some disinfectants to clean the plants while they are in the vessels - you need to do your own research, I never needed the experience.

The water is not really crystal clear - it's a little milky.

The mechanical filtration media is not dense enough. As a final stage, you might want to add a very dense sponge (or similar material), to collect even the small particles.

I had a very similar problem, and I was lucky to find for buying a piece of "cloth" - the dark green layer which is glued on one side of kitchen cleaning sponges. I added a layer (or maybe 2 layers? I do not remember) between the sponge and the pump (everything inside the filter). The aquarium with this trick was functional in excess of 3-4 years, long lived fishes, all nice, cleaning of the filtering media max 2-3 times per year.


Were you sure to wash everything thoroughly before adding them to the tank? Even new items/plants need to be cleaned off before adding.

I believe you possibly have some variation of thread algae. Thread algae survives on decaying organic matter within your tank. Generally these are removed with a thorough tank clean but on most occasions they are harmless to the inhabitents anyway.

Some things you can do to combat this:

  • Reduce the time your tanks lights are on
  • Do a big tank clean,
  • Introduce some Amano shrimp,

For more information you can check this out it's a really informative wiki page.

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