30 Gallon Tank Troubles With Anaerobic Bacteria And Root Rot In Low Tech Tank

Hello,

I am struggling to grow root plants in a 30 gallon low tech tank thats been running for a few months. I am hoping someone more experienced can lend some advice.

The tank has pool filter sand that is 2 inches deep. I have been using root tabs and dosing the water column with fertilizer to about 10 ppm Nitrates.
I know 10ppm Nitrates might be a bit low however, I had these plants growing well with that amount in a quarantine bucket that only had ambient light. Plus I figured the root tabs would mainly be enough to grow the plants. I am using NilocG Thrive liquid fertilizer and nutrition capsules as well as some flourish root tabs that I had left over. I have also been dosing the tank with the recommended dose of Seachem Excel every morning. I have not had plants melt from the Exel. I slowly increase the dose of excel in quarantine over a few weeks before adding plants to my tank to help avoid this.

Today I decided to investigate further and uprooted some plants only to find that the roots where black and starting to rot.
I stirred up the sand and realized that the lower layers of substrate had turned from light beige to black. I suppose this is anaerobic bacteria.
Could this bacteria be causing the roots to rot?

I actually added more plants today and raked through the substrate with some tweezers. The tank is also suffering from a soft brown algae outbreak, could this be being made worse by the anaerobic bacteria? I am planning on reducing the amount of blue light the tank is exposed to to hopefully help control the algae.
The tank is lightly stocked.

Advice is very much appreciated!

 

I stirred up the sand and realized that the lower layers of substrate had turned from light beige to black. I suppose this is anaerobic bacteria.
Could this bacteria be causing the roots to rot?

It sounds like anaerobic bacteria to me. And, yes, I believe it (or at least the conditions that cause it) can cause root rot. I've found it's sort of like a race with sand. If you can get lots of healthy roots in the sand, the roots seem to aerate the sand and make it ok for the plants. If the roots do not get established quickly enough, they tend to die in the anaerobic conditions. That's my hypothesis anyway.

I'm not too sure what to do about it once the sand gets all black short of starting over. But, I would guess it could be addressed over time by stirring the sand regularly, getting sand stirring critters (like MTS snails), and getting some hardy, big root type plants (like crypts or swords) established where you can.

I think the most sure fire way to fix the issue would be to replace your substrate with plant soil (and then top it with a thin layer of sand if you like).

 

I think those flourish tabs are like 15% calcium, 12% sulfur and black like coal. I had a friend using those and when we uprooted his tank before he moved it was a stinky mess.

In a pool filter sand substrate you should have plenty of aeration, especially at only 2" deep (filter sand doesn't pack and suffocate like moon sand, that's why they use it in filters). It's possible the plants were getting too much nutrient and the roots were dying back, or that the plants just weren't healthy in that tank yet.

I really don't think you would have full on anaerobic in 2-3 months anyhow. Even when we try to grow it on purpose for de-nitrification reactors etc it takes months and months (if ever)in optimal conditions. Additionally in my limited experience, I have a few tanks running 3+ years on PFS, only deep vacuuming the sand every 3-4 months and adding fresh sand on top to intentionally trap the detritus/nutrients. The pool filter sand in those are 3-5" deep, biggest difference is I don't use those black root tabs. The friend offered me his after we gutted his tank and I casually (ok, with some flair) put them in the trash. The black ash like clouds they put up in the tank made it even harder to catch the clown pleco and otto's, which were why we had tried to pull the plants first anyhow lol.



To get that junk out, try plunging your siphon into the sand, once the sand has filled the bell part partly kink the hose, then let just enough water flow to tumble the sand. Kink it the rest of the way to let the clean sand fall out then move over a bit and do it again. Not too hard, I have done my less planted tanks like this since I started.

 

Thanks for the replies everyone!

Yesterday I turned over some of the sand so that blackened sand was at the surface of the substrate. The more time that goes on that sand is changing back to beige. I also have the exact same sand in other tanks and have noticed that some of the sand turns black in those tanks as well and I have never used root tabs in them. However, in those other tanks I have catfish and cichlids that dig so the blackened sand is usually only under large stones or caves and I only see it when moving things around to clean. Does that seem like it might be bacteria then?

For now I cut any mushy dead looking roots off and replanted the tank, I also did add quite a few more root plants yesterday so hopefully that will help if it is anaerobic bacteria. The leaves on all the plants still look great so hopefully they bounce back! I keep raking the sand and will try aerating with the siphon as suggested.

I really appreciate the help, I’m not so good with plants!

 

It sounds like you are dosing the fertilizers pretty heavily. Is there a specific reason, do you have plants that would require dosing of ThriveG and Excel beside the root tabs?

 

It sounds like you are dosing the fertilizers pretty heavily. Is there a specific reason, do you have plants that would require dosing of ThriveG and Excel beside the root tabs?

I only Fertilizer enough to bring Nitrates up to 10-15ppm. The amount is still under the recommend dosage for their liquid fertilizer. This tank has mainly stem plants but also has some rhizome plants that are attached to drift wood. From what I understand many stem plants can still benefit from nutrients in the water column is that true? The stocking is very light so I dose with excel to give the plants more usable carbon and to help inhibit algae from taking hold. I also dose with Seachem equilibrium because my tap water is less than degree hardness. I do a 50% water change once a week to stop minerals from building up in excess and do a closer to 75% water change once every month or so.
Thanks for taking time to read through