Phew! What A Smell

Every time I sit and gaze at the aquarium, the gazing interlude is preceded by a visual glance at the main equipment – heaters, skimmer and the like. I also do this just before I feed, it only takes seconds and becomes second nature.

So there was I, defrosted brine shrimp ready for the fish, and my eye wandered around the aquarium equipment as usual. What attracted me to it I don’t know. I’d not noticed it earlier.

In the back bottom right hand corner it lurked. Dark and threatening and definitely not wanted. Some beast that had crept out of the rock?

No, much more simple than that. It was a patch of smear algae, sometimes called blue-green algae (which makes it sound quite pleasant, but it isn’t), also called Cyanobacteria.

This unpleasant stuff likes areas of low seawater flow, and sure enough it was in such an area. It also needs nutrients.

Out came the phosphate (PO4) and nitrate (NO3) tests. The tests showed ’undetectable’ for both. Perhaps there is a trace in the seawater but the tests aren’t sensitive enough?

Anyway, somewhat reassured, I removed the stuff with a stiff toothbrush. That’s about all that can be said for it, it isn’t particularly difficult to remove.

If there is any nutrient, why is it not being controlled? The skimmer operates as usual. All pumps etc are fine.

Then I noticed. I’m not sure if this is the reason, and if it is it seems a little illogical.

The drip rate from the output of the sulphur denitrator was exceedingly slow. One drip every few minutes! How could I have not noticed!

Anyway, I decided to clean the denitrator and ensure it functioned properly. I remembered the ‘nil’ reading from the nitrate test, but this must be because of the live rock. The pump was stopped and all feed/exit pipes disconnected. The tube containing the sulphur beads was taken into the kitchen.

I took off the sealing plate at the top of the tube and started to pour out the seawater. Wow! The smell was incredibly horrible, like rotten eggs that weren’t satisfied with being rotten and so double rotted. Yuk.

With this lovely un-aromatic stench around my head I emptied the tube and cleaned everything. All windows and doors were opened (good job it was a sunny day) causing my wife to come in, attracted (no, that’s got to be the wrong word) by the smell. An explanation was given, and she didn’t hang about but went back to the sweet air of the garden. The smell hung around the house for ages, even though fresh air had been given entry.

The problem, of course, was hydrogen sulfide, which gives itself away by the very distinctive rotten egg smell. The flow of seawater through the denitrator had been so low that the hydrogen sulfide had the opportunity to develop.

The denitrator was set up again, and I was about to switch it on and begin the process to re-establish the bacteria. Then I stopped and closed the flow taps.

There wasn’t a reading of nitrate on the test. The rocks in the aquarium are live. So why use the denitrator? The live rock must be doing its job.

I’ll have to monitor for nitrate regularly for a while, just in case the denitrator had taken any load off the live rock – perhaps the live rock will need to get up to speed.

So why is there a denitrator present anyway?

The answer is that when the aquarium was started 5½ years ago, the rocks that I used weren’t live. They were inert and highly porous, and over a long period they have developed into live rock – the holes, crannies and surfaces becoming the home of many tiny marine creatures, including of course bacteria.

So despite the fact that I have an inbuilt routine when feeding livestock or admiring the reef, perhaps the routine had become too rigid.

Lesson learned – I’ll not be caught a second time. I hope.


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