[resonator]

So my first planted tank has been up and running for about a month. I decided to start out in a very low-tek fashion. Basic specs are: 25gal hex, 36w 6700K/1000K compact fluorescent lighting, pool filter sand, no C02, yada yada.

The substrate was purchased in a 50lb bag from a local swimming pool supply store. I only used about half of it (or less). I had to rinse it out several times, but I think the size is about right (based on Rex Grigg's recommendations). Substrate depth is just under 2".

Rex's recommended sand size...

My sand size... fairly close, if not just a tad smaller.

However, lately I have noticed some menacing looking black spots at the bottom of my substrate.

The bottom (from underneath the tank) looks like this...

I was almost certain these were anaerobic pockets. Then I remembered that when I added the substrate approx. 1 month ago, I also stuck in 4 or 5 flourish tabs. My purpose for that was to nourish the substrate without adding any potential messy laterite, flourite, peat, etc... Being that this is my first try at a planted tank, I wanted to go easy on myself.

I've had a previous non-planted run with this tank using some very fine sand, and these black spots developed spontaneously (no tabs obviously), and when I dismantled the tank, they had the sulfur stank which I've came to understand to be an anaerobic bacteria outbreak. I'm very concerned that this could be a repeat performance, or perhaps it's just the dissipating flourish tabs and I'm overreacting based on my previous experience. I have done a bit of plant re-arranging over the course of this past month (as I said, I'm still learning), so perhaps that accounts for some of the dissipation of the tabs.... i hope?

Anyone want to weigh in? Is there a way I can test without risking potential harm to my tank's inhabitants?

 

[Storm_Rider]

oooh i hate that! its the stink from hell i tell you!! could be the tabs, but i'm gonna guess that the tabs started to rot in the sand and caused the anaerobic pocket.

now i'm concerned because i have a tank of fine sand up to 3 inches deep X_X

 

[Rex Grigg]

Ok, to start with that picture in my Guide is the MINIMUM size sand I would use. By going smaller you will will have problems with the sand compacting.

Also by placing the Flourish tabs in this fine sand you have provided the bacteria with nutrients and large amounts of sulfur. So what you see there are the anaerobic pockets that you fear.

I also notice how few roots you have showing in the bottom of the tank. The one tank that I can see the bottom of is my 55 gallon and it's covered in roots.

 

[resonator]

Okay, so I need to replace my substrate. Shoot.

Okay, I'm happy to do that if it means long term success. However, I'd like to know a reliable way to get quality small gravel of the right size without having to buy a 100lb bag, only to be disappointed by it not meeting recommended size requirements. Any recommendations?

Or... could I get away with just one inch of the same pool filter sand I've been using as long as I use plants that aren't heavy root feeders? A shallower substrate level should decrease compaction and subsequently the chance for anaerobic activity I'd think.

Should I forget the flourish tabs altogether? I thought they were recommended for those in my situation who didn't want to be bothered with a messy "first" layer.

I will also plant more rooted plants to get my substrate a bit more oxygenated.

Any other advice?

 

[Tsquare]

Rex are you saying the Flourish tabs are a problem in the fine substrate? I hope so as I just got a 10 pack today but haven't put them in there yet. My substrate is larger than your min size. Probably 3 to 4 mm grain size.
Gene

 

[resonator]

Where are you people getting these ideal inert substrates? I thought bona-fide pool filter sand would be the holy grail. Obviously I was wrong. I just want something nicer looking than the garden variety Estes stones you can buy at PetStoreCo, Inc.

 

[confuted]

You could try just stirring up the sand a bit, and then getting some MTS which will go through and burrow into the sand. Personally, I'm not convinced by the whole 'minimum grain size' argument. I've never seen a place in nature with plants growing in such large grain sand; they are invariably in much finer stuff. I understand that natural environments have a lot more going on than happens in the aquarium, but I'm using sand that I dug out of a riverbed. Bubbles come up occasionally, but so far, there aren't any problems.

 

[Rex Grigg]

In a river setting you have current flowing through the sand. Our tanks can't come close to nature.


resnator: Any place that sells bags of sand and gravel should have samples you can look at before you buy the bag. You might have to ask to see them but they have them.

Flourish tabs work fine in a larger grained substrate.

 

[resonator]

update!

Udate: It's almost been a year since I started this thread. I have not changed the substrate out during that time, although I did stir it up a little bit with a small gravel rake a couple of times not too long after I composed the original post. But by and large I have left it alone, or let the cory catfish do the work on the very top 1/4" layer of the gravel.

Anyhoo, as you can see, the dark spots have disappeared for the most part on their own, and some roots have flourished as well, so I'm guessing that what I was seeing in the original post was just the flourish tabs dissipating/dissolving into the substrate. If it had been anaerobic bacteria, I'm thinking my tank would have been in much worse shape than it has been this past year, and the spots probably wouldn't have improved on their own.

 

[lauraleellbp]

Have any roots actually growing through the spots? (there's a little glare on the pic so I couldn't quite tell?) This just a guess on my part, but by my way of thinking, if the spots were just the fert tabs you should be getting lots of root growth there, but if the tabs decomposed and there were anaerobic spots, roots won't grow there?