Diatoms question

danieljones8623 · Nov 29, 2021

Hey there,
So, I guess I’m having the same issue a lot of others have when starting a tank. I have, pretty sure anyway, diatoms. I is RODI water and I’m assuming it mostly due to me not rinsing my sand off and having a large amount of silicates still. That being said, I’ve read that it’ll likely take time for the silicates to be depleted from my system in order to fix the situation. My question is, what causes the silicate to be depleted? Through regular water changes? Scraping the glass and the diatoms being skimmed?

boacvh · Nov 29, 2021

I am not an expert but a picture may help to see if its diatoms or something else, but diatoms are a pretty normal stage for a new tank.
My understanding is yes, all of the above will help. The diatoms themselves "consume" the silicates to build their cells and as they get consumed or exported the silicates will get depleted. WCs will help reduce silicates as long as your WC doesn't have higher silicates. If your RODI is working properly you should be ok on that. GFO also removes silicates.
However, if its indeed diatoms, I say just let it take its course, no major harm will come from them and part of ugly stages to get to a balanced tank anyway, so I would just be patient. FWIW I actually dose silicates in my tank now after I had a short fight with dinos.
Experts will chime in soon though.

danieljones8623 · Nov 29, 2021

Here is a pic. I don’t think I really have super bad problem with it at the moment (knock on wood), it could get much worse though. I’ve had them for the past several weeks. They’re ugly, but I’m just sticking it out the best I can. Through research though, some of the post I’ve read say they “just go away”. That just made curious as to how this happens, mainly how does silicate just get used up? Unless you’re taking it out, wouldn’t it always be in your tank?

boacvh · Nov 29, 2021

danieljones8623 said:
Here is a pic. I don’t think I really have super bad problem with it at the moment (knock on wood), it could get much worse though. I’ve had them for the past several weeks. They’re ugly, but I’m just sticking it out the best I can. Through research though, some of the post I’ve read say they “just go away”. That just made curious as to how this happens, mainly how does silicate just get used up? Unless you’re taking it out, wouldn’t it always be in your tank?

Yes, I wouldn't worry about these for now, looks like a regular ugly stage of new tank to me. Just keep doing what you are doing and wait for a few weeks and see if there is any improvement.

And you are correct, unless you are taking them out in some way they are still in your tank. But they can be in a form that is not necessarily available to be used by other organisms (i.e. "new" diatoms can't absorb silicates from the water column that have already been absorbed by other diatoms to build their cells). As your CUC or your skimmer or other mechanical filtration removes diatoms, you are removing those absorbed silicates from your tank as well. As long as you aren't introducing higher silicates with the WCs than your tank has (with a proper RODI you likely aren't), then diatoms start to become limited by the availability of the silicates in your water column.
tagging @Randy Holmes-Farley here who is the expert and has a great article on Diatoms and Silica, but for the life of me I couldn't find the link. (he will also correct me if I gave you wrong info)

tharbin · Nov 29, 2021

While it is hard to be 100% sure from the photo that looks like a very mild case of diatoms. Nothing to worry about it will burn itself out in time. If it starts to become a bigger issue come back on and ask for some advice on minimizing the bloom but it is completely natural and normal.

Just do your normal routine except I would not stir the sand bed to try to eliminate the diatoms. That will just bring fresh silicates to the surface. I typically sift 25% or less of the sandbed during a water change. A couple of Nassarius snails will also help as they gently stir the sandbed as they move through it. Cerith and Trochus snails will consume some diatoms and conchs are a diatom bulldozer.