i have 2 ornaments in the tank which are growing brown marks, is this algae and how would i treat it? every day i check and the marks have grown. The light is on for about 10 hours on average.
Is your tank in direct sunlight at all. Too much direct sunlight can cause brown algae.
No algae eating fish will touch the brown so you may have to remove the ornaments and wash them by hand. If it persists you may have to reduce the amount of direct light in the tank, reduce the amount of artificial light per day, or use a bulb with less wattage
Some algaes are the result of elevated levels of phosphate or nitrate. You may want to test these levels and increase the frequency of your water changes if they are high.
Brown algea is normally caused by a lack of light although it can also be a sign of super hard water,but you are right no fish will eat brown algea so it does have to be removed by hand.
To prevent it coming back increase the lighting in the tank to at least 2 watts per gallon ie 10g=20w.
i now have green algae mixing with the brown on the ornaments! the wattage of the light is 18w and the tank is around 20 gallon. my tank is still at the cycling stage so will washing the ornaments by hand remove valuable bacteria and should i wash them in tank water?
Removing the algea wont affect the cycling of the tank and yes you should only wash them in tank water,to double the output of your lighting tube fit it with a reflector available from any lfs.
The green algea will be eaten by any algea eating fish you choose to add,i would recomend 3 or 4 otocinclus (species depending on what is available in your lfs) which stay small and consume huge ammounts of algea.