Silicates too high, Diatoms return

[neilanh]

So, I went through the normal diatom cycle when I first set up the tank. They ran for a while then burnt themselves out. Now, they're back. Water test confirmed silica is elevated in my tank.

How do I reduce them?

I was under the impression that GFO, while removing phosphate, would also remove the silicates too to some degree, but I've been running GFO non-stop and they're coming back. I recently recharged my reactor with fresh GFO, so maybe that'll help.

But, what else can I do? My sand bed is back to looking like dirt.

 

[AMDPhenomX4]

What kind of sand did you use?

 

[neilanh]

Aragamax dry sugar-sized oolite

 

[thincat]

Neilan, maybe sugar fine is to fine and the silica is slowly leaching out of the bottom layers of your sand? Just a thought...

 

[roka64]

I believe some oolite sand can be high in silicates (I think I remember that from geology class). The diatoms should burn them out over time. Until then you may have outbreaks.

 

[Kurt_Nelson]

You say you tested. What were your silica levels? And did you test your fresh salt water? Don't forget... many salt mixes will have silica levels in them that may be considered "high", or at least above normal.

 

[ccCapt]

I use oolitic sand...I highly doubt thats the source. If you haven't done it yet, I would try changing the DI resin in your RO/DI unit.

 

[Innovator]

I know people hate algae, but it's a part of life. It will always be there and as you mentioned before, eventually the diatoms will burn themselves out. I disbelieve anything is leaching from the substrate, far stretch imo considering you're using aragonite. Salt mixes that incorporate silica probably do so sparingly and depletes readily imo. As others have stated and probably what you've done by now, check the source water to make sure any resins have not expired and clean up your substrate...you filthy animal.

 

[CaptainAhab]

and clean up your substrate...you filthy animal.

lol

 

[thincat]

+1...that's a really nice comment too...LOL

 

[neilanh]

What was tested was not my freshly mixed water, but rather water taken from my tank 2 days after a PWC. The Silica (SiO2-3) level was measured at 0.9 mg/L. This is the test done by aquariumwatertesting.com. They claim acceptable levels are below 0.5 mg/L, just for reference.

I'm ok with cleaning my sand, maintenance, etc. I'm just confused in that I had already gone through my normal diatom cycle, they burnt themselves out and havent been around for many months. now all of a sudden they're back, and much stronger than the first time.

I must be feeding them is all I can come up with. Coming from my RO/DI water? perhaps. DI resin gets changed on about 60 day centers, so I believe that I'm doing all I can there. I use colorchanging resin and swap out fresh resin when a) the color changes out or b) I get any inkling of >0 TDS in the water, whichever comes first.

Is there anything else that can be done to remove the silica to stop feeding the diatoms?

 

[roka64]

Are you using a DSB? If so, the released air can react with the silicon and form the silica (silicon dioxide)/diatoms....
If you don't have a DSB, maybe try a different brand of DI resin....?

 

[Kurt_Nelson]

Neil,

Look at aquariumwatertesting's report on their site where they tested the salt mixes. You'll see that most salts average right up around 0.9 mg/l. So it's not coming from anything you do... it's coming from the salt.

I just recently sent a sample in to them also... just to double check my numbers. My silica levels also came back at 0.9. And I also run phosphate remover 24/7. Some of the other numbers seemed a little whacky, but it's all relative.

In the end, with all salts testing at that level for silica (whether or not the number is correct!), we ALL most likely have a silica "problem". Personally, I think you're chasing a ghost problem that really isn't there. Diatoms come and go, especially in a new tank. And yeah... your tank is still new!

 

[thincat]

Are you using a DSB? If so, the released air can react with the silicon and form the silica (silicon dioxide)/diatoms....
If you don't have a DSB, maybe try a different brand of DI resin....?

Roka, can you explain further about "the released air can react with the silicon and form the silica (silicon dioxide)/diatoms",
What air are you talking about??? I thought that the DSB breaks nitrates down to nitrogen and that is what is released from the Sand bed.

 

[neilanh]

Kurt, that's a good find, I hadn't thought to go look at the salt comparison that they did.

That being said, so what you're saying is that it's not uncommon for diatoms to "come and go" as they wish? I was under the impression that diatoms was a factor of new tank syndrome, if you will, but that once you did a cycle on them (mine lasted >2 months) that you should be good going forward. I also believed that the fuel for them was *typically* a new tank having ripe, fresh silicone being used for the bonding of the seams, that this was the source and hence why diatoms would burn themselves out after consuming all of the food from the fresh silicone.

Anyway, all that aside, I'm just still puzzled a bit. My tank is something like 10 months old. Still new? ok, it's all relative, don't want to argue that point.

What I'm trying to understand in my head is since I went through my diatoms 'cycle', they burnt out and went away for > 5 months, and now they're back, what changed? I keep up on my maintenance, weekly 25% PWCs, keeep the skimmer clean, don't overfeed, etc. Why are they back now and why weren't they present last month? I'm just having trouble justifying all this in my head. If the food source is the salt mix that's maintaining the 0.9mg/L, then why did they ever go away?

 

[Kurt_Nelson]

Well... all I know for sure is that there's a TON of stuff biologically and chemically going on in our little closed ecosystems that no one really understands. Even the experts. Understanding the ocean is one thing, but our tanks... totally different. So why diatoms come and go? Can't tell you. All I can tell you is that they come and go, and not on a regular basis, in my tank. And I think many folks with old tanks still have them come and go - for no apparent reason.

Hey... my tank is three years old, and I still consider it a "new" tank! Until you stop adding things to a tank, every new addition has the potential of changing the balance of things, and making it "new" all over again! At least that's my take on it...

And don't be afraid to vacuum the top layer of the sand!

 

[neilanh]

Fair enough. I do vac the sand, take off the top layer. It's just that eventually I'll have no sand left, will have to add replacement sand, and start the cycle all over again. lol

 

[roka64]

Thincat, I was just throwing that out there, I think Kurt may have got it.
To answer your question, you will see bubbles that rise from the DSB that contain an amount of O2 and I was just guessing that may have been enough to feed the silicates. I don't have any hard number, was just thinking out loud....

 

[thincat]

I thought that the bubbles were the last cycle of the nitrogen cycle and that would make the bubbles nitrogen. Correct me if that's wrong.

 

[roka64]

You are correct, but nitrAtes = NO3, so you have 1 Nitrogen atoms bonded to 3 Oxygen atoms....ahh, I see what you are saying.
Sorry I got my molecules and atoms mixed up....I think I was thinking the bubbles meant O2....I stand corrected...Sorry for the confusion and nice catch!