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Discussion Starter #1
Hello,

I have recently acquired a second tank for my classroom: a figure 8 puffer fish + 3 bumblebee gobies. They are a big hit, and seem to be doing well. I got the entire set up from someone who was downsizing. The substrate is crushed coral. I've noticed a lot of algae growing on the surface of the substrate, but when I tried a gravel vac all I did was make a big cloudy mess. The algae seems to be sort of a green skin, so vacuuming just broke it into pieces but didn't suck it up. In the meantime, brown algae has started growing on the glass.

I've never had a brackish tank, and I have no idea how to clean this. My other classroom tank is a planted guppy tank. Algae is not an issue: there are plants, and a cleaning crew. But for the brackish, what's the solution?

Thanks for any suggestions!
 

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It sounds like diatoms and cyano bacteria. Cyano (slime algae) usually starts growing in tanks with low flow and high organic build up. I would try using your water change regime to 50% a week and adding a circulation pump or an HOB filter with purigen as a chemical media. Diatoms are usually a sign of new tank syndrome or changes in lighting sources. Is the tank now facing south facing window or getting more ambient room lighting? Just some thoughts.

Best regards,

Stuart


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Discussion Starter #3
Hi Stuart,

The tank is far from windows, but there's lots of ambient light: it's a classroom. I turned off the light and wrapped it in black felt fabric for the weekend; we'll see if a few more days of that maybe will help any. Organic buildup is a likely factor, since puffer fish are slobs, haha. I didn't know that low flow would be another factor to consider. I will look into getting Purigen – I've never used it before – and do a better job with the water changes. I'm also looking into what plants can do well in brackish water, though I had read last week that they may not do as well as in freshwater without additional CO2. As this is a classroom tank, I'd rather stick to inexpensive solutions where possible, haha!

Thanks for your thoughts!

Any idea how to clean the algae that's already all over the crushed coral? Will it go away on its own with my improvements? It looks terrible right now.
 

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The slime algae (cyano) can be tricky to remove from crushed coral. I believe gravel washing it and increasing flow will help. I believe adding purigen will hopefully be the 1-2 punch you are looking for. If this does not help, you may need to eradicate it using erythromycin (this is really hard on your bacteria colony). I would first try improving your water quality. There are a number of salt tolerant plants you can add too (https://www.petcha.com/brackish-plants/).

Best regards,

Stuart

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You can get rid of the cyano by simply temporarily shutting off the filtration, lowering the water level to facilitate your spraying full strength H2O2 (regular household hydrogen peroxide) unto the cyano at close range, using a plastic syringe or test kit pipette.
It will form bubbles onto the cyano which will eventually disperse up to the surface, a sure sign that it's working. If you can't do all of the cyano at one go ( say up to a dozen sprays or so with the H202 ), you can repeat the procedure the following day. The cyano you have sprayed on day one will disappear by the following morning. Turn the filter back on in about a half hour after spraying so as not to remove the bubbles too soon before they've had a chance to do their job.

To keep the cyano from returning, as Stuart said earlier, improve your water flow (and thereby oxygen levels) at or near the substrate level by adding a water circulation pump, or at least a power bar. (Cyano only survives when oxygen level is low or non-existent.)
 

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Discussion Starter #6
Thanks for this info! Will the H2O2 treatment harm the fish (1 F8 puffer + 3 bumblebee gobies)? Should I stick them in a bucket while this gets done?

I've had the tank blacked out for a week. In the meantime, I've purchased Purigen and will hopefully be able to set everything up and try these other steps next week.

Still not sure about gravel vac on the crushed coral: last time I tried, I couldn't find the gobies for a full day because of the cloudiness, and when it all settled there was still bits of algae all over the surface that I had missed. Clearly I suck at sucking!
 

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I've only done the H202 treatment twice over the years, and it hasn't harmed the fish at all.
But I've been careful to not overdo it at one time - that's why I suggested not more than about a dozen sprays on a single day - and repeat next day if necessary - to be on the cautious side. I haven't read anywhere where it can harm fish, as it dissipates very quickly into the water column - but no sense pushing the envelope.

I suppose it could possibly harm fish that were near to where you're spraying and the spray went right at them - in my experience though, the fish will stay clear of where you're working the syringe. Scatter them if they come close.
 

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I have been prepping a brackish tank for Opae Ula and have the same green film algae growth. One Zebra nerite and he's going through the stuff like a champ. My water is at around 15ppt salinity. Nerite adapted from fresh water no problem.
 

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Discussion Starter #9
Update: I blacked out the tank for about 10 days, scrubbed all the glass, did a 50% water change, and replaced filter media with a couple of mesh bags full of Purigen. I tried gravel vacuuming the substrate but because it's crushed coral, not sand, it was sucking up the dust and leaving the heavier clumps of algae, which is the reverse of what I wanted! I ended up hand-picking the bigger chunks, and just turning the rest over to hide it.

I added a couple of marimo moss balls and a bigger clump of java moss, and also stuck the light on a timer because I kept forgetting to turn it off. This was maybe 2 weeks ago. The glass and substrate are starting to show signs of brown algae again but not nearly as fast as before. The plants aren't looking too happy, but they aren't dead yet either. I've turned off the light for Winter Break - no one'll be there to look at the tank (custodian will feed) so no point making it pretty and encouraging more algae growth!

I've only done the H202 treatment twice over the years, and it hasn't harmed the fish at all.
I suppose it could possibly harm fish that were near to where you're spraying and the spray went right at them - in my experience though, the fish will stay clear of where you're working the syringe. Scatter them if they come close.
Heh, the puffer likes to follow my hand around when I stick a finger in the water. Silly fish! I haven't tried H202 yet; I may have to yet... we'll see how the tank looks in Jan.

I have been prepping a brackish tank for Opae Ula and have the same green film algae growth. One Zebra nerite and he's going through the stuff like a champ. My water is at around 15ppt salinity. Nerite adapted from fresh water no problem.
I was thinking of getting a Nerite, but I know puffers eat snails. Would he eat a snail the same size as him??
 

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The puffer won't eat the snail...in one bite. I wouldn't recommend it - sorry, forgot that you mentioned you had a puffer in the tank.

It's a tricky situation w brackish water tanks because of the lack of suitable plants. I've had pretty good luck with fresh water tanks since mine are heavily planted.

You might want to try MTS...they also adapt pretty easily to brackish water and generally work ok w puffers since they only come out at night when the puffers are sleeping. If the puffers do start eating the MTS just keep an eye on their beaks... MTS shells are pretty hard.
 

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Discussion Starter #11 (Edited)
The puffer won't eat the snail...in one bite. I wouldn't recommend it - sorry, forgot that you mentioned you had a puffer in the tank.

It's a tricky situation w brackish water tanks because of the lack of suitable plants. I've had pretty good luck with fresh water tanks since mine are heavily planted.

You might want to try MTS...they also adapt pretty easily to brackish water and generally work ok w puffers since they only come out at night when the puffers are sleeping. If the puffers do start eating the MTS just keep an eye on their beaks... MTS shells are pretty hard.
Hmm. I have MTS in another tank (and an assassin snail to try and keep the population down); I had considered putting some in the puffer tank for the puffer to eat, but had read their shells are too tough. It never occurred to me to put them there for algae because they can resist the puffer! Also, I didn't know they were brackish adaptable. Hm.

Would the puffer damage his beak trying to eat MTS? How would I even know, or help, if he did? Brackish tanks are certainly tricky! I'm used to fresh water planted, too.

The algae has been slower to come back since I changed the filter media, put the lights on a timer, added a water pump thing, and more moss. We'll see how it looks in Jan (our awesome custodian is feeding the fish over winter break, I'm a lucky teacher!)
 

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I expect that in most cases the MTS will be in hiding when the puffer is out and about...that's what happens in my tank. Once the lights come on the MTS zoom into the substrate. I'm not familiar with the larger puffers, but I know the dwarf puffers generally just bite the exposed foot etc portion off. I'd imagine that damage to the beak would be relatively rare cases, given that their beaks ARE designed to deal with shells.
My algae is almost all gone now - too much in fact. Have to hunt for the MTS and remove the nerites. The nerites laid eggs which is what I was after - let's see if the eggs hatch!
 
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