Possible cyanobacteria in understocked tank?

Zonotrichia

For the past year+, I've been dealing with what I think is a mild but persistent case of cyanobacteria in my planted 29 gallon tank. The tank is cycled, but has been extremely understocked since January (1 guppy). Our bioload is negligible, and nitrates are persistently 0. The plants have also been suffering from a lack of nutrients and care. It's been a hectic year and we'd been neglecting the tank except for feeding our one fishy fellow and doing water changes and half-hearted vacuuming every 2 weeks or so.

Anyway, we have a light-colored sand substrate, and for a good portion of the last year, it has been getting covered in a kind of grey/blue cast. See below pictures as well as one from August 2020. Sometimes it looks more brown, sometimes darker or blue-ish spots appear on the sand. It seems to clump, but it doesn't really come off in sheets like I often see described with cyano. It has that swampy, earthy smell, which is what made me think it could be cyanobacteria. It is also extremely hard to siphon up; we've ended up losing a ton of sand in an effort to get rid of it.

I tried dosing with Ultralife Blue-Green Slime Stain Remover (2 doses 48 hrs apart, then again this week, per instructions), but I'm not sure if I've seen a noticeable difference.

The tank has been running since March 2020. Parameters are Ammonia 0, Nitrites 0, Nitrates 0, pH 7.4. I haven't tested GH and KH in a while, but our water is very soft and we supplement with crushed coral and Equilibrium. We dose with 1 pump of Easy Green during cleanings, but again...we've been neglectful. The light is a standard Aqueon LED hood, on for 8 hours each day (using a timer). For filtration, we have an AquaClear 70 and a sponge filter. Plants are anubias, java fern, crypt spiralis, amazon sword. As you can, they're not doing too hot anymore :\

My questions:

1. Does this look like cyanobacteria to you? If so, or if not, how best to deal with it?
2. I know our tank is unbalanced and needs a bunch of TLC. We're currently QTing some new corydoras and want to make this the best possible home for them. How do you suggest that we turn this tank around?
 

Flyfisha

Hi Zonotrichia,
That is not Cyanobacteria. It looks like an ordinary algae to me with some lose mulm .

There are lots of algae killing chemicals sold for aquariums . If you intend to keep shrimp get a shrimp safe mixture.

You ask about turning the tank around.
It is perfectly safe to change 50% of the water every day. Vacuuming up what you can . A link below on how to vacuum without removing any sand.

Even with fish in a tank you can still vacuum 59% every day or every 4 hours after the fish have adjusted to the new water.

 

Zonotrichia

Yeah, I wasn't worried about the loose mulm, more the way the greenish-gray stuff seems to coat the top of the sand. It never seems to progress to a slimy/stringy texture, just keeps coming back and looking unpleasant. Probably because my tank is unbalanced, and that's what happens!
 

Cherryshrimp420

How much Equilibrium are you adding? Crushed coral will add GH which overlaps with Equilibrium so Im curious how you determine the dosing amounts...
 

DoubleDutch

Looks like diatoms. Think you're giving yourself the right answer. Plants need (some).nitrates, phosfates, other ferts, light and CO2 to grow and get the tank in balance.
 

Sobhan

These look like diatoms not cyanobacteria. Use some seachem excel every couple of days unless you have vallisneria it will melt any type of vals. If your stocking allows you to have otos and nerite snails keep them, they will clean evrything up in a few days.Or a single hillstream loach will also thrive with eating the algae if your flow is good.
 

Zonotrichia

How much Equilibrium are you adding? Crushed coral will add GH which overlaps with Equilibrium so Im curious how you determine the dosing amounts...

I’ve been keeping 1/4 cup of crushed coral in my filter since I realized that my tap KH was basically 0-1 dKH and making it difficult to maintain a stable pH. It seems to have settled at around 3 dKH.

For GH, I’d been dosing 1/2 Tbsp during water changes to get it up to ~8-10 dGH since my guppies had been struggling so much. To be honest, I don't think I had noticed a super noticeable increase in GH when I was just using crushed coral. I’ll check the GH/KH at the next water change to see where I'm at (when I’m not cooking all day).

These look like diatoms not cyanobacteria. Use some seachem excel every couple of days unless you have vallisneria it will melt any type of vals. If your stocking allows you to have otos and nerite snails keep them, they will clean evrything up in a few days.Or a single hillstream loach will also thrive with eating the algae if your flow is good.

We’ve been on the fence about how to build a clean up crew, though I know the tank would benefit! Will probably settle on Nerites, but the prospect of constant egg cleaning is a little unappealing. I love how otos sound, but I don’t think we will have enough space for a nice school for them to be happy. Our current plan is Corydoras sterbai (6 currently in QT), school of harlequin rasboras, one or two honey gouramis if I can find them, and our solo guppy for as long as he lasts. Temperature is kept at around 78, forgot to mention. (So, too warm for hillstream loaches.)
 

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