Are diatom and brown algae the same thing?

[plecc833 2]

Hi all.
To my limited knowledge, diatoms are a microscopic organism encased in a silica shell. That thrive in a high silicate/phosphate environment. Please correct me if I'm wrong!
Is this what others are referring to when they use the term "Brown Algae" or is brown algae a completely different issue?

I am curious because I'm having a persistent ongoing issue with brown stuff developing all over my anubias and wood, the brown stuff has a red/brown tone to it very similar to the colour of the rosewood but a little brighter, it only appears in the better lit areas. Sometimes as a thin dusty like coating and others as blotches over the leaves. It can be removed fairly easily with your thumb or a toothbrush.
the tank also has a bit of black beard algae around the edge of some of the older leaves.

Aquarium = 120L (4Ft) with Fluval 305 canister
Substrate = Pool filter sand (supposedly 95% silica)
Hardscape = Loads or Rosewood (the rosewood is many years old, it no longer leaches any tannins. It could be contributing to high phosphate)
Plants = Various Anubias only
Lighting = Very low for 8 hours a day
Stocking = Very low 2x zebra loach, 8x Sterbai Corydoras
Schedule = Weekly 25% water changes, filter cleaned every 2 weeks

I don't currently have a test kit for silicates or phosphate, but happy to pick one up if required. Can someone advise the most logical way to try and track down the source of this problem? Thanks.

 

[Naughts28 100]

Maybe brown algae could be an inaccurate term for diatoms but I am unsure in what context you heard it? If you post a photo of your “algae” someone will identify it. Your description of red-brown stuff that can be rubbed off could well be Cyanobacteria.

 

[fishthatfit]

Yes, brown algae is the common name for diatoms. Same thing, and your description of the silica shell is right.

Two things though. Pool filter sand won't be your silicate source. That is quartz, and quartz barely dissolves at tank pH, so it sits there inert; the silicate that actually feeds diatoms comes in with your tap water. Test the tap, not the tank.

And the light pattern argues against diatoms anyway. They do best in the dim corners and usually fade as a tank matures, whereas yours is only where the light is good. Before buying any kit, rub some off and smell your thumb. Cyano gives itself away that way, and it lifts as a sheet rather than smearing into dust.

 

[plecc833 2]

Thanks for the feedback,

I was trying to research the problem on youtube, but to be honest this left me with more questions than when I started. Some of the youtube lot were using the terms diatoms and brown algae to mean the same thing, while others were saying that they are two completely different issues.
I have seen cyanobacteria a few times before in other tanks, I'm fairly certain that's not the issue but I imagine cyano can crop up in many different forms and colours. I will try and get a pic up later once the tanks lights are on.

Thanks for clearing that up fishthatfit,
I have been using pool filter sand for years now with no issues, under the assumption that it was almost inert, especially in a hard water tank.
But again one of the youtubers I found was making out that all silica based sand was the devil!

Am I correct in thinking that a tank with a pH 7.5 and a high carbonate/general hardness is very stable against water chemistry change from hardscape. While a more acidic soft water tank with a pH of say 5.0 and low hardness would likely see significant change due to leaching?

I was thinking that my water supply was the issue.
To be honest, my description regarding lighting may have been misleading. Thinking back the main reason its concentrated under the light is due to the way I've been cleaning, the tank has a wide brace across the centre which makes cleaning the plants in this area much more awkward. This area of the tank also has lower flow.

Is the best coarse of action to pick up a silicates test kit?

 

[plecc833 2]

Here is the current state of the tank, apologies for the poor photo. I was finding it quite tricky to get a clear shot without loads of reflections.
Hope this helps.

 

[fishthatfit]

Your reading of the buffering is right, though the direction is worth naming. Carbonate rock dissolves fastest in acid, so in a soft pH 5 tank hardscape pushes hardness and pH up rather than down. In your water it is already close to saturation and barely dissolves at all. Quartz sits outside both cases: its solubility only starts to matter somewhere above pH 9, which no freshwater tank sees.

I would skip the silicate kit. There is no number on it you would act on, since you cannot strip silicate without RO or a resin, and tanks stop having a diatom problem because something else outcompetes them rather than because the silicate ran out.

The low flow behind that brace is the more useful clue in your last post.

 

[TwoTankAmin22]

Rather than write it all out, here is what the AI tells us:

In a home aquarium, cyanobacteria behaves like an algae but is actually a photosynthetic bacteria. It is infamous for growing in thick, slimy sheets or mats that easily peel off surfaces.
Its color depends drastically on whether your aquarium is freshwater or saltwater (reef):

1. Freshwater Aquariums
In freshwater tanks, cyanobacteria is almost universally referred to as Blue-Green Algae (BGA):

• Deep Blue-Green / Teal: This is the most common variety. It forms a smooth, dark green or turquoise blanket over plants, substrate, and glass.
• Blackish or Gray-Green: A darker variation that often cakes over the gravel or sand in low-flow areas.
• Dead / Dying Cyanobacteria: Turns a pale, milky white or light turquoise as the cells break down.

2. Saltwater (Reef) Aquariums
In marine tanks, it is usually called Red Slime Algae:

• Deep Red or Purple: The classic reef variant. It covers rocks, sand, and even corals in a velvety burgundy or violet sheet.
• Rusty Brown or Black: Often confuses hobbyists because it looks exactly like a bad diatom outbreak, but it forms cohesive, air-bubble-trapping sheets rather than a dusty powder.

How to Confirm It is Cyanobacteria
Apart from the color, you can accurately identify it by two distinct traits:

1. The Smell: Cyanobacteria has a highly distinct, foul, earthy, or swampy odor. If you pull a small piece out of the tank, it will smell intensely like a stagnant ditch.
2. The Texture: Unlike true algae (which clings tightly to glass or rocks), cyanobacteria is incredibly slimy and can be easily wiped or siphoned off in large, fragile sheets

 

[plecc833 2]

Good stuff!
Thanks fishthatfit,
Do you think I would be ok using some seiryu stone in one of my small tanks, given my water pH 7.5 and a high carbonate/general hardness?
Oh, I had no idea that was the case with the silica test kit. So it doesn't actually have a unit scale like say PPM, is it just a colour scale to indicate if silica is present?

So, do you think the best course of action would be to add some plants that grow a bit faster than the anubias and try to improve flow around the centre of the tank?

Thanks TwoTankAmin,
That's a great break down of cyanobacteria, it makes me pretty certain that it must be diatoms.

 

[raylove]

If the problem persists then I highly recommend the silicate removal resin.
My source water varies but can be as high a 3ppm silicate. I suffered diatoms for nearly 50 years (to some extent) and was always advised that silicate removal would make no difference.
However, a year ago, when the problem had become particularly bad, I decided to give it a try. After 9 weeks (changing the resin at 3 week intervals) the diatoms were gone - silicates had fallen to 0.1ppm.
I now test regularly and put the resin back in for a few days if the levels rise above that level.12 months on there has been no recurrence of the diatoms.

 

[gwand28 144]

If the problem persists then I highly recommend the silicate removal resin.
My source water varies but can be as high a 3ppm silicate. I suffered diatoms for nearly 50 years (to some extent) and was always advised that silicate removal would make no difference.
However, a year ago, when the problem had become particularly bad, I decided to give it a try. After 9 weeks (changing the resin at 3 week intervals) the diatoms were gone - silicates had fallen to 0.1ppm.
I now test regularly and put the resin back in for a few days if the levels rise above that level.12 months on there has been no recurrence of the diatoms.

What brand of resin did you use? Thanks.

 

[TwoTankAmin22]

I am a big fan of anubias. I have been keeping them since my very first tank went from fake to live plants withing the first two years of doing artificial plants. They also get algae, btw.

Over the years I have had anubias get so that they no longer fit in any of my tanks without being at the surface. What I learned with time is that the taller they got the more algae they would get. The problem is that anubias grow much more slowly than algae. As the plant get closer to the light it will get ever increasing amounts of algae.

I have had a red algae problem on the anubias in my clown loach tank for many years. As I upgraded the tank size the algae moved along with everything else.

I have done all kinds of planted tanks over the years and never had to battle algae so hard in one tank. I had not done floating plants in a very long time until last fall when I won some Amazon frogbit at a club auction. Today it is in almost all of my planted tanks. I have so much of it I sell it at the club auctions and throw out a lot of it as well. One of things I have noticed is that as the amount of it in any tank will soon become a total cover on the surface. So I am having to remove some every week.

What has also happened is that algae levels in all the planted tanks has decreased. The excess nutrients that the algae was able to use is being sucked up by the frogbit. So, now I have a frogbit problem rather than an algae one. The difference is that I can scoop up and throw out frogbit a lot easier and way faster than I can deal with algae covering anubias leaves.

As for diatoms these have never been an issue for me. So I asked my old friend Google, "how persistent can diatoms be in a planted freshwater aquarium" and here is what I got back which may or may not be helpful as I cannot vouch for its accuracy.

AI Overview

Diatoms usually last 2 to 6 weeks in a brand-new freshwater planted aquarium before vanishing on their own. [1]

Typical vs. Persistent Lifespan

• • New Tank Phase: In a fresh setup, brown diatom dust peaks around the 2-week mark and clears up within a month or two once silicates in the new sand or glass drop and beneficial bacteria take over. [1, 2]
  • Chronic/Persistent Phase: If high silicates or continuous nutrient leaching occur, diatoms can stubbornly persist for 3 to 6 months or longer. [1, 2]

Why They Overstay Their Welcome

• • Silicate Leaching: Tap water rich in silicates, or the use of certain new quartz/silica sands and rocks, continuously fuels their cell walls.
  • Low Water Flow: Dead spots with poor circulation allow the brown film to rapidly settle and blanket slow-growing plant leaves.
  • Immature Biome: A lack of competing green algae or robust microbial life lets diatoms dominate. [1, 2, 3, 4, 5]

How to Clear Them Out

• • Manual Removal: Gently brush or wipe them off plants and glass right before performing a water change.
  • Cleanup Crew: Add algae grazers like Otocinclus catfish, Amano shrimp, or Nerite snails which eagerly consume them.
  • Improve Circulation: Increase water movement to prevent settling in dead zones.
  • Source Water Check: Switch to RO (reverse osmosis) water if your tap water tests excessively high for silicates.

(edited for typos)

 

[raylove]

What brand of resin did you use? Thanks.

I used Phosguard.
There's a potential issue in that this removes phosphates too, and in a planted tank that might cause a deficiency. In fact I sometimes have to dose phosphate if my plants show signs of phosphate deficiency and if I had to up the dose then I thought that might exhaust the Phosguard quite quickly.
In the event none of that has actually happened. I continue to add phosphate every few weeks. My plants grow a little slower than they did before, but that's no bad thing as they were quite high maintenance previously! Also the older leaves no longer fall victim to the brown 'algae' so the look much healthier and grow bushier.
The reason I chose Phosguard is because the dedicated silicate removers I saw were all said to be quite messy. Given what I'd read I hadn't really expected this to work so I took the easiest route! When I next have to buy some more remover I might try one of the others now I know it does work. I'm not using as much as I thought I would because it seems that once my high levels are reduced they stay low for some time after I remove the resin. I'm thinking that maybe my tap water contains different levels at different times of the year depending on where they are drawing the supply from.

 

[fishthatfit]

Seiryu should be fine in your tank. It's a calcareous rock, so it gives up carbonate fastest in soft acidic water. Yours already sits at pH 7.5 with high KH, so there isn't much gradient left for it to work against and it won't move your numbers far. Soft water tanks are where it actually does something.

On the silicate kit, that was badly put on my part. It does give you a ppm figure, colour matched against a chart. What I meant was that the number wouldn't change what you'd do next.

 

[plecc833 2]

Wow thankyou everyone!
Apologies for my slow reply, things were a bit crazy last week.

Thanks Raylove,
I have been looking into the various types of silicate removal products.
Seachem - Phosguard and Phosbond
Arka - Sili-Out 2 and Phos-Out 4
JBL - SilikatEx and a few others.
All appear to also target phosphates as you mentioned. I'm a little concerned that my phosphates levels are already very low. The tanks plant growth has been extremely slow over the last 12 months.
My substrate is plain old filter sand. I don't use any liquid nutrients or root tabs, I don't use a gravel vac anymore. I clip out most decaying plant matter weekly, the tank has a low stocking for it's size. I mostly feed various pelletised foods, sparingly once daily. Filters are cleaned every week or two depending upon size.

Some of my plants do have pinholes but only on the most mature leaves.
But honestly I'm just guessing that phosphate levels are very low, so I have ordered one of the NT Labs phosphate test kits to help me get a better understanding of my tank and water supply levels.
Raylove,
You mention dosing phosphate while also using the resin, I had thought about this but quickly dismissed it because I also expected any liquid fertilizers to rapidly deplete the resin. But that's excellent to hear that you didn't notice any issues.
Do you just dose exclusively phosphate or did you mean as part of a complete liquid fertilizer?
It sound like you dose phosphate as required based on "if your plants show signs of phosphate deficiency". What is it exactly that you look for to determine that phosphate levels are too low?

One thing I did notice is that the silica capture resin used in RODI systems, does appear to exclusively target silica without affecting phosphate levels, could this possibly be used in say a canister filter?

Thanks TwoTankAmin,
I'm also a big anubias fan! I struggle a bit with the dwarf varieties, but all of the other larger leaf anubias are just so hardy and easy to work with. Another plant I have had great success with in the past is cryptocoryne wendtii, planted into aquatic net pots filled with regular pond soil and a bit of gravel on top. They do tend to melt back and look dead for some time while they adjust to the new conditions, but given a bit of time they explode in growth. I had a couple that grew so big they started coming out the top and almost completely shut down water flow from one side of the tank to the other.

I have played around with a few different floating plants in the past, but in my tanks they typically do quite well for a few weeks, (I guess surviving on stored nutrients) and then start to decline and slowly loose colour becoming almost glass like in appearance.
Also, all of my planted tanks quite quickly develop an oily/mineral film on the surface that requires some sort of surface agitation or a skimmer to keep in check. Keeping this film under control while trying to keep the plants topside dry proved to be quite tricky.
But I would defiantly like to give them another try in the future, any tips would be greatly appreciated.

Thanks for the diatoms breakdown, I would say that the tank is stuck in the "Chronic/Persistent Phase" experiencing "Silicate Leaching" from my water supply. About a week ago I repositioned my outflow Improving flow across the plants, which does appear to have helped the situation a bit. I fear I may be also experiencing "Immature Biome: A lack of competing green algae or robust microbial life" there isn't any noticeable green algae.
Do you think I could kick the tank out of this phase using some of that bottled filter bacteria?

Thanks Fishthatfit,
Oh that's great! I was hoping that was the case, I will get some seiryu stone ordered.
Ah, I see what you mean regarding the silica test kit, thanks for clearing that up.

 

[plecc833 2]

The Phosphate test kit arrived today,
Phosphate = 0.5ppm
Silicates = Assumed to be high.
Nitrate = 15-20ppm
Ph = 7.5
The above readings were taken at the end of the week just before maintenance and water change.

After having a thorough check earlier, my anubias are really starting to struggle. a lot of the leaves are yellowing quite considerably. The small amount of new growth is very pale and almost transparent.
BBA is starting to take hold on some of the older growth, and the brown algae is still terrible requiring a few hours cleaning each week.

Is it a bad idea to use Phosguard to bring down silicates when my phosphates at 0.5ppm?

How can I feed the plants without just making the algae worse?

Thanks