Diatoms are a kind of unicellular algae that has the characteristic of having an outer silica shell, so they need silica to grow, contrary to other algae. They are really fast growers, and for this reason they are dominant where silica is present, like river estuaries. They actually produce 20% of the oxygen around the world.
Why am I telling you this? Simply to let you know that if you have silica in your aquarium you are gonna have diatoms, and if you have diatoms silica is present.
Now, this isn’t something bad, I dose silica when diatoms aren’t present, so does Randy although I do not know his schedule. Silica is also used by sponges and other organisms and can be healthy for a reef tank. Also, it’s consumed really fast as shown
in this article by Randy.
Silica can enter an aquarium via water changes (salt mixes do have silica present) and via RO water. A reverse osmosis membrane do not filter silica out (in the form of silicic acid) very well, the resin will. So a resin that’s beginning to get exhausted will let silica through. Not only will it let it through, it will leach the silicic acid trapped, so expect a burst of silicate as a first sign of a exhausted resin.
From
Randy’s article about RO/DI systems:
“It turns out that
silicate is found at the lower end of affinity for anion resins. Consequently, if the DI resin has been collecting silicate for a long period and is then depleted, a large burst of silicate may be released.”
By the way, this fast usage of the silica in an aquarium also means that it won’t get trapped in a sand bed in any usable form, so that’s not your problem here if indeed what’s growing are diatoms.
If you want to get rid of this, your culprits might be your salt mix (which I’m guessing you didn’t change), a higher frequency of water changes (which also I’m guessing you didn’t change) and the water you are using.
