Rock/substrate hwlp

Charlie G · Sep 12, 2025

Hi all,

Wondering if anyone can help describe what’s going on in my 32g Biocube. I’ve had this algae issue (I think it’s algae) covering my rock and sand for a couple of months now. The rock looks like it’s carpeted with with brownish red substance. It’s starting to develop on some of my coral (Cyphastrea and lepto). As well once a week as it gets close to my weekly water change I develop this ‘bloat mat or mucous’ formation on my sandbed. Occasionally bubbles form on it.

I clean the sand once a week and that keeps it away until about day 5 or more after my water change. I do a weekly 4.5 g water change weekly siphoning the sand as well. I also seem to be developing brown dust like coating on my glass daily.

I do have vermatid snails all over but that’s been there for much longer than this current issue.
My parameters are as such.

SG 1.026
Nitrate 3.2
Phos 0.06
Alk 10.1
Ca 456

I have inverts such as trochus snails, cerith snails, bumble bee snails and a couple of hermit crabs.

I don’t have the ability to totally clean my sand other than siphoning weekly. I do try to brush some of the rock weekly as well.

Any advice is greatly appreciated.

BonnieB · Sep 12, 2025

Charlie G said:
Hi all,

Wondering if anyone can help describe what’s going on in my 32g Biocube. I’ve had this algae issue (I think it’s algae) covering my rock and sand for a couple of months now. The rock looks like it’s carpeted with with brownish red substance. It’s starting to develop on some of my coral (Cyphastrea and lepto). As well once a week as it gets close to my weekly water change I develop this ‘bloat mat or mucous’ formation on my sandbed. Occasionally bubbles form on it.

I clean the sand once a week and that keeps it away until about day 5 or more after my water change. I do a weekly 4.5 g water change weekly siphoning the sand as well. I also seem to be developing brown dust like coating on my glass daily.

I do have vermatid snails all over but that’s been there for much longer than this current issue.
My parameters are as such.

SG 1.026
Nitrate 3.2
Phos 0.06
Alk 10.1
Ca 456

I have inverts such as trochus snails, cerith snails, bumble bee snails and a couple of hermit crabs.

I don’t have the ability to totally clean my sand other than siphoning weekly. I do try to brush some of the rock weekly as well.

Any advice is greatly appreciated.

Can you do some white light pics? In this pink light it looks like Cyanobacteria (plus the fact you say you can blow it off) but white light pics would help people responding to be certain! Also what are your parameters, lighting and flow?

Charlie G · Sep 12, 2025

Hi. Thanks for responding. I want to correct. It doesn’t blow off easily. Some fragments of the rock covering come off but I really have to brush it off and that is not that easily removed. I will attach pics with white lights.

My parameters as of yesterday are listed above.
My lights are Biocube lights. My light schedule is:

BIOCUBE LIGHTS
1-Whites 10:00-19:30
2-Ramps. 9:30-20:00
3-Blues/Moon 9:30-23:00

I also have 2 21LEDUSA strips CH1 (blue/actinic) (Full intensity.

On time 9:30
Off time 19:00
Sunrise/sunset (ramps) 15 min
Min intensity 10%
Max intensity 100%
Moonlight 4 hours

I have 2 Hygger wavemakers (will show pics).

Hope this helps

Charlie G · Sep 12, 2025

Ignore the last pic. Lol

the schwartz · Sep 12, 2025

What are your nutrient levels?

Charlie G · Sep 12, 2025

As of yesterday:

SG 1.026
Nitrate 3.2
Phos 0.06
Alk 10.1
Ca 456

BonnieB · Sep 12, 2025

I think we’re looking at multiple things. GHA, colonial hydroids, and cyano. I could be wrong but that what it looks like from the new pics.

BonnieB · Sep 12, 2025

Charlie G said:
Hi. Thanks for responding. I want to correct. It doesn’t blow off easily. Some fragments of the rock covering come off but I really have to brush it off and that is not that easily removed. I will attach pics with white lights.

My parameters as of yesterday are listed above.
My lights are Biocube lights. My light schedule is:

BIOCUBE LIGHTS
1-Whites 10:00-19:30
2-Ramps. 9:30-20:00
3-Blues/Moon 9:30-23:00

I also have 2 21LEDUSA strips CH1 (blue/actinic) (Full intensity.

On time 9:30
Off time 19:00
Sunrise/sunset (ramps) 15 min
Min intensity 10%
Max intensity 100%
Moonlight 4 hours

I have 2 Hygger wavemakers (will show pics).

Hope this helps

How long are you at 100% intensity each day?

Charlie G · Sep 12, 2025

About 9.5 hours full white.

BonnieB · Sep 12, 2025

Charlie G said:
About 9.5 hours full white.

Algae and hydroids grow exponentially with a lot of light, especially high intensity for long periods of time. I think that is possibly the cause of the explosion since your nutrient levels don’t seem out of control.

Charlie G · Sep 12, 2025

Trying to understand hydroids. Is that the reddish brown substance carpeting the rock or the vermatids/tubes?

Should I try a period of lights off or maybe only blues? I’m concerned about the corals. But at the same time as you can see in the pics I think it’s invading my coral especially the Leptoseris and the Cyphastrea

Mr. Mojo Rising · Sep 13, 2025

How many fish do you have and what is your filtration like? How much and how often do you feed?

I would think that you have very high level of dissolved organics in your water for the tank to be that green. Do you have a protein skimmer? If no skimmer, then you should increase the amount of water you change.

You do very minimum water changes of 4.5 gallon... when you have a bad algae problem like this you should increase the amount of water changes, even multiple changes per week. Scrub the rocks and blow them with a turkey baster while you siphon water out.

Charlie G · Sep 13, 2025

I have 3 fish. I only feed once a day.
No skimmer. Just biologic filtration and filter floss in second changer of this AIO.

I do try to scrub the rock with my water changes. As it is a biocube it is has to get all around the rock.

Mr. Mojo Rising · Sep 13, 2025

The filter floss should be changed every 2-3 days or else it will hold rotting food which releases more organics into your water.

I feel that organics is the main issue, and since you have no skimmer you should increase the water changes as the only way of removing the organics. Organics (DOC's) are the kryptonite of reef tanks.

This is a great article that helps explain in more depth the role that DOC's play in our tanks. Good luck

DOC is The Most Important Parameter For A Healthy Reef Tank: Here’s a New Method to Manage It | Reef Builders | The Reef and Saltwater Aquarium Blog

In this article, I will provide an overview of my take on the current zeitgeist of reefing and explain why the entire industry is ignoring a critical aspect of coral care. I will explain what issues…

reefbuilders.com

Charlie G · Sep 13, 2025

I will read the article. Thank you for your input.

Charlie G · Sep 13, 2025

Do you think a black out period also help my current state in addition to the increase in water changes and scrubbing the rock? I’m worried at it’s affect on coral.

Tikki · Sep 13, 2025

Are you mixing your own water or buying? Maybe time to change out RO filters. Have you checked that return pump is flowing well? If you have sponges in the back make sure they’re not full of crud. I squeeze mine out in bucket of tank water during water changes. I would pick up more hermit crabs and reduce white light for a bit. When you say you’re scrubbing the rock wdym? Do you pull the rock out or just try and break it loose with toothbrush? Looks like maybe a few things in there dinos maybe cyano and algae. I would make sure source water is good and make sure pump is clean and working well. Sometimes they slow down and need to be replaced after couple years. Are the bio cube lights fluorescent or led? CFL bulbs may need replacing also if they’re older. They will keep lighting up but spectrum can change with time.

Charlie G · Sep 13, 2025

Mr. Mojo Rising- thanks for the article. I have heard Sem speak several times on different podcasts as well as reefbuilders. I do enjoy his content and knowledge. I will implement some suggestions.

Tikki-

Thanks for responding. Great pioints.
I mix my own water but have not changed out my RO filters. I have been thinking about it and trying to figure out when I need to. My TDS Comes out at zero so I thought (possibly because I have a 32 g BioCube and do 4.5 g water changes weekly that I have not used them up) but I have had the same filters since I set it up.

The return pump seems to be flowing well.

I don’t have sponges or don’t think I do. lol. Sorry for being naive here. I’ve had the system for about 3 years now but still learning. Do you purchase sponges and where would I put them in an AIO Biocube. I presume they need to be devoid of light (2 nd chamber???). Salems article makes good points at the effectiveness of sponges on DOC.

I will reduce the white light. Any suggestions of how long I should keep the white lights on per day as to not adversely affect corals?
I can keep blues.

I use a toothbrush although recently I pulled my top rock out and scrubbed it.

The Biocube lights are LED.

Thanks. I appreciate the suggestions.

Tikki · Sep 13, 2025

Oh, OK. You’re welcome. I had a bio cube some years ago when they were relatively new. I don’t recall what the set up in the back was like but all of my other all-in-one aquariums have had sponges. I think it would be good to change out your RO. I know on mine I replace the sediment filter every six months and the RO and other cartridges about once a year. I mentioned the return pump because I know for me that has definitely been an issue in the past they keep working and I even take them out and clean them, but they’re not flowing nearly the gallons per hour that they did when they were new sometimes it’s hard to tell, but if you’re totally relying on that as you’re main only filter might be worth picking up a spare and trying it out. I’d be temped to start there and refresh the clean up crew and see if things improve.