Everyone here is talking about their own experiences and not giving an actual reasoning for why diatoms appeared now.
Yes, they probably are diatoms, what color is the film algae in your glass when you clean it? Green or brown? If it’s brown then it’s almost certainly diatoms.
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.
You said you are using water from someone else, and you trust them. I’m not questioning they knowledge, just letting you know that the resin they use is probably beginning to exhaust just now, and this would be the first sign of it. Furthermore, they may not even consider it a problem, as I said before, some people dose silicates.
As a bit of extra information, the discrepancy about disturbing or not the sand bed is because in anoxic places (more common in deep sand beds) hydrogen sulfide may form, which is highly highly toxic and if much of it is released it may kill your whole tank.
Hydrogen sulfide reacts with oxygen, so it’s a good practice if you are gonna disturb the sand bed to do it when oxygen is highest, after midday in your tank. This correlates when pH is highest in your tank.
Most sand beds today aren’t really deep so there isn’t a lot of risk of this happening, but another good idea is to, if you are gonna do it, disturb the sand bed by sections, and not all of it at the same time.
You can read more about hydrogen sulfide in yet
another great article by Randy.
Lastly, and as a bit of anecdotal information, I’ve have a sand bed for over 20 years and I do not siphon it. I might occasionally disturb sections of it. The only algae’s present in my system are coralline algae and diatoms, mostly in the glass.
But then again I’m well aware this is anecdotal information, and as such is not worth much. Everyone here should keep that in mind about their own experiences too.
This thread expands on this.
https://www.reef2reef.com/threads/r...-experience-to-accept-or-reject-truth.368374/
Good luck and keep us posted!
It’s always nice to have a conclusion to a thread!