aaronnorth said:
If you have silicates in your water then it may never go.
It continues to astound me that we perpetuate this theory without any proof or without even questioning why this should be.
Think about this for a moment: Popular aquarium sediments are constructed of inorganic silicate compounds. Clay, such as Aquasoil is a type of "Phyllosilicates" constructed of aluminum/silicon/oxygen molecule arranged in parallel sheets. Sand is typically made of quartz which in the family of "Tectosillicates" and is also an aluminum/silicon/oxygen molecule but arranged in geometric lattice. Quartz is one of the harder substances known. It actually ranks slightly higher in hardness than steel. There is about as much likelihood that the silicate molecule will leach into the water column from quartz sand as would the silicon dioxide molecule of which your tank's glass is made of would. So in effect silicates in the tank never go away as long as you have glass, clay or sand in the tank yet diatom algae is not currently present in all those tanks. I can add kilos of sand to my tank and this will not spark a diatom algal bloom - so this theory must be either false or incomplete.
While it is true that Diatom algae use silica to build their cell walls (known as frustules) the origin of the silica from diatoms in an aquarium has not really been verified. Their uptake of silica must be in the form of the various forms of silicic acids such as H2SiO3. This can only occur by chemical reaction of silicate salts present in the water column. It is more likely that these salts are either in the tap water or are leached from the plants themselves due to poor nutrition. Plants uptake silica salts as well and in terrestrial plants the silica is used to strengthen the cell walls to toughen it against pest attack (
as demonstrated in this paper ). The salts are made available by the reaction of humic acids in the soil with any available silica salts to form silicic acids.
Still, the presence of silica salts in the water column by itself does not induce diatom blooms. This is a false correlation. Something else induces the algae which then feeds on whatever is available in the environment. There is a greater probability that the issue is poor nutrition, principally poor CO2 or poor CO2 distribution, as the OP reports algae on the leaves. Blaming excess silicates for diatom algae is about as unreasonable as blaming excess nitrates for BGA.
I would increase the frequency of large water changes, remove by hand, add more flow (or rearrange the piping) and
carefully increase the injection rate.
Cheers,