Need so help with water flow

[machine646]

Ihave a 20g long glass tank with a 160ghp and 500gph powerheads,but i still keep getting alge on my sand bed and on my rocks,the sandbeds is a redish color alge and grren alge that look like slime if i take the rock out of the water,my water perm a ammonia0 nitrite 0 nitrate 20ppm before water change,also where are the best places to place the powerheads? how much flow should i have ? im plaining on keeping softies and a pair of clowns.Right now in the tank is a clown,hermits and bumblebee snails.

 

[Peppie]

How long has your tank been running? Might just be a normal algae cycle your tank is going thru

 

[machine646]

its been running close to 3 months

 

[Aquanaut]

Part of new tank symptoms. Helps keeping more cleaner crews to stir up surface, perhaps adding a cucumber, hermits, emerald crabs. Monitor and keep Magnesium 1500 will help too. Sometimes changing photoperiod can aid to stop the event. Clue, Do you notice the red diatoms disapearing nightly only to return progressively in the daytime? Can you increase skimming to lower nutrients feeding it.

 

[akunochi]

It is your natural algae cycle. Cut your lighting back slightly and find the cause of nitrates. Nitrates and light are feeding this algae.