Dead spots

[platypus]

I have heard a few people mention 'dead spots' on other posts - just wondering what this is and how do you know if you have one and what do you do to get rid of it?

Thankee kindly

 

[Alien Anna]

Hi, sadly this is a subject I came to know a lot about

Basically, if some of your substrate doesn't get enough oxygenated water to it, the beneficial bacteria die off and are replaced by nasty, anaerobic (oxygen-hating) bacteria that produce sulphur dioxide as a waste product. The sulphur dioxide forms a gas pocket which when disturbed by a bottom feeding fish, for instance, dissolves into the water instantly as sulphuric acid and... goodbye fish

Dead spots generally form under rocks, tank ornaments or bogwood, which is why you should move them around every once a while and clean underneath them. If you ever smell a smell of rotten eggs in your tank you need to react immediately to clean up the problem before your fish die - I lost quite a few fish when this happened to me.

The problem is that once you have sulphur dioxide gas bubbles and sulphuric acid in your tank, it will harm your fish before you have much time to do anything about it. 100% water change and paranoia for weeks afterwards is the only way I know to fix it. In the end, I swapped out my entire gravel and had a bit of a hairy time putting my tank through a mini-cycle (this is not fun when you've got rummynosed tetras and pencilfish). Since then I've always told people who inheirit and old tank to do a total strip down if at all possible, whilst keeping the filter and some of the top gravel to avoid the tank having to cycle all over again.

Anyway, prevention is better than cure so make sure you give your gravel a periodic sort-through to aerate it and don't have it too deep. Plant roots, once established, will help keep the substrate aerated.

 

[Lateral Line]

I found silver sand compacts and can form dead zones, thus, as Anna said, you need to do a bit of "gardening" to keep your sand open. I got around this by using swimming pool filter sand. This does not compact and there is enough circulation, (without help - more later), to prevent anoxia.

To improve circulation in my old set ups, I used to use "UltraTherm" under tank infra red heater pads, deliberately under rating them so the substrate remained largely, but not totally still. I found that Dennerle heating cable worked better because there were warm areas and cold, thus convection drew water through the substrate.

I have tried without either, with the filter sand, and have no problems.

 

[Lithril]

If you're starting from scratch and want to avoid it totally you can alway put an UGF under the gravel with the out put from the pump going into it so it pushes an waste and gas etc out of the gravel and gets taken into the filter, works a treat.

 

[New Boy]

Would I be right in thinking that gravel is less likely to develop dead spots? I still don't think that there is any substitute for ensuring that you move round bits of your gravel. I've been away from fishkeeping for nearly ten years but I remember being told that was one benefit of gravel over sand in teh old days.

I tend to do a gravel clean a dffierent area of the tank at each water change - except the bit where I've got loads of live plants bunched in one corner - so that at least once a month the gravel gets moved.

 

[Lateral Line]

>>>
UGF under the gravel with the out put from the pump going into it so it pushes an waste and gas etc out of the gravel and gets taken into the filter,
<<<

Reverse flow, yes, this can be a poweful technique, and would almost certainly stop anoxia in a gravel tank. Points...

1) This does not work well with sand substrate, the sand works it's way into the ugf plates and over a period of time increases the resistance to flow of the pumps output, this can then overheat and die.

2) Assuming a gravel bed, the return water takes the path of "least resistance", therefore areas under stones for example will not be circulated.

3) If you are using the output from a canister which has a heavy biological filter, the water you are forcing up through your gravel is Oxygen depleted, so any beneficial bacteria that might otherwise exist in your gravel bed is starved of Oxygen.

 

[Lithril]

Toying with the idea for my next tank but havent decided on a substrate yet. Some filters let you add an air supply on to the output, wonder if I could combine these so that the water was freshly oxygenated. Probably going to be getting an Eheim ECCO on the the good advice of AA had a look at them an I'm definately impressed.

 

[guppymonkey]

I heard that sand makes a terrible substrate because it compacts, which causes those dead spots to appear. Sounds like a good argument against sand to me. Gravel has larger spaces for water to flow.

 

[mrV]

You can easily break up bottom monthly or put some snails to your tank (those snails look like ice-cream cones and live in bottom.. So they are caretakers in aquarium. They keep sand loose enough and prevent sand becomes blocked)

It's same with gravel too. If you don't vacuum it enough, silt becomes blocked too.

 

[Alien Anna]

You can easily break up bottom monthly or put some snails to your tank (those snails look like ice-cream cones and live in bottom.. So they are caretakers in aquarium. They keep sand loose enough and prevent sand becomes blocked)

It's same with gravel too. If you don't vacuum it enough, silt becomes blocked too.

Snails? Wot snails?

I don't have many snails - just a couple of the fattest loaches you've ever seen