Been bugging me for years...

[deckard_wa]

I hope I manage to explain this question properly, so please bear with me.

Conventional wisdom has always been that after the nitrifying bacteria have done their bit, the end product is nitrates, and there is NO way to get rid of the nitrates except by doing PWCs, which I and everyone else have been doing diligently (I hope!) for years. No arguments yet? Good. This is where it gets complicated. Take for instance Lake Malawi in Africa. I have never been there but I understand that it's a rocky environment with precious few plants and only algae growing on the rocks, and that this algae is eaten my Mbuna. Even though this lake is absolutely huge and in reality an inland sea, it is thousands if not millions of years old. In that time there must have been untold billions of fish in that water, all producing ammonia that eventually becomes nitrates. My understanding of evaporation is that only water is lost, so if a lot of evaporation happens the levels must get even higher, only falling back again when the rains come. So, where do the nitrates go?

There have been a lot of sleepless nights pondering on this, and I can think of a few possibilities, but does anyone out there better informed than me know for sure?

[Slinky_Bass]

Good question! As far as i know ther are other ways of removing N03 apart from PWC's, check out this link:

http://saltaquarium.about.com/library/blank/bl_myths.htm

As for your question about lake malawi, this is my understanding of how N03 levels are regulated. Once the nitrifying bacteria has done it's job, and nitrates are building up in the lake, the increae of nutrients (N03) will lead to what we are familiar on a small scale, algae bloom. This algae grows and multiplies in the presence of increased N03, the more N03, the more algae blooms to feed off the nutrients. The fish in turn eat some of the algae, but for the most part what happens is that the algae grows and consumes the N03 so fast that the N03 rapidly becomes depleted and the algae dies off as quickly as it came. My understanding and explanation of this natural cycle is very simplistic I realise, but I'm pretty sure that's basically what happens. During elevated N03 and algae levels there might be deaths amongst fish populations, but then a corresponding boom in babies will fill the gap.

The conversion of N03 to nitrogen gas is another way of getting rid of N03, but from what i understand, this only happens in anaerobic conditions, so not suitable for Aquariums.

Anyway, that's my take on it, what possibilities were you thinking of?

[deckard_wa]

Well, I thought that maybe there's a run-off to the sea somewhere (have to be a long river I know), or that there's some bacteria that do eat nitrates.

I read somewhere a while back an article about some research that has been going on in Germany for a few years. It was late at night and I was tired so I can't remember the exact details and I forgot to bookmark it. The gist of it was, I think, that we do not yet fully understand the nitrogen cycle, and that there are more bacteria in play than we realise. Apparently preliminary findings seem to suggest that doing too frequent water changes can actually be harmful as these other bacteria are slower growing and I think live in the water, and are removed at PWC time. Like I said I can't exactly remember all of it, but I thought maybe this had something to do with it too.

If there's a natural element out there that's removing nitrates and it can somehow be utilised in the home aquarium, it's gonna make someone a whole lot of money, not to mention saving a lot of fishies lives.

[Slinky_Bass]

I think we don't even understand half of how our world works yet, so it stands to reason that there might be some as yet unidentified bacteria/organisms/organic processes that regulate N03 in nature. It's a real pity you didn't bookmark that site, it sounds like some interesing reading. But now that I know it's there somewhere on the net, maybe it can be found again.

[deckard_wa]

LOL yeah it's out there somewhere. I don't even remember how I got there because I was just surfing, going from one link to another. I think I started on the internet movie database and 4 hours later ended up on a fish research site!! Funny how everything comes down to fish in the end with me.

Your explanation of the algael blooms seems like a reasonable one, though, so I might go with that for now

[Fishguy2727]

There are anaerobic bacteria that turn nitrates into nitrogen gas (N2) and at that point the nitrogen leaves the water and becomes part of the atmosphere again. Lake Malawi has deep regions that are anaerobic (in fact I think by volume it is the largest part of the lake) so most likely that is how it is maintaing itself. The algae wouldn't actually remove it from the lake because the fish eat it which then turn it right back into ammonia and start the whole thing over again. In saltwater aquariums these anaerobic bacteria can actually keep up with the production of nitrates and you can have a truly complete nitrogen cycle. These denitrifying anaerobic bateria live ON surfaces just like nitrifying bacteria, so they won't be affected by water changes. In saltwater tanks they usually live in live rock, but a plenum is a very good way to make sure there are enough to keep up with nitrate production.