Tropical Fish Keeping - Aquarium fish care and resources

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MrWynO14 05-22-2010 02:17 AM

Alarming Information
I just read some very alarming information that I didn't believe at first but makes perfect sense. This website claims that water changes do not offer a long term solution to nitrates in the aquarium unless you have plants and/or denitrator and/or change 100 percent of the water. It gives a chart and shows that 50 percent water changes over time gradually keep the nitrate rising, slowly but surely. What do you guys make of this?????

iamntbatman 05-22-2010 03:44 AM

Not very alarming. The problem with their math is that it assumes that your fish are producing nitrate faster than they're being removed. If that is the case, then yes, you would have a problem, but under normal circumstances you don't let this happen. Either 1) don't overstock the tank so much that water changes can't handle the nitrate production, 2) do more water changes to handle the nitrate production or 3) get more live plants. Using their math, if they simply did two 50% water changes a week nitrate would never accumulate.

MrWynO14 05-22-2010 06:35 AM

But if you change 50% water to cut the ppm in half, then add fresh water back in, then do another 50% water change it should still have some nitrate in the tank right? Two 50% water changes doesn't equal one 100% water change correct?

MrWynO14 05-22-2010 07:08 AM

20 cut in half is 10, then 10 cut in half is 5, then 5 cut in half is 2.5....

Basically, If you don't have plants or a denitrator then eventually you have to change more water than normal, or do more frequent water changes just to get the ppm back to a low reading. Wether "eventually" may be every 6 months, or every month, depending on your tank and what you have in it.

Kim 05-22-2010 07:52 AM

Yes, the actual math is sound, but an aquarium is not a cut and dry equation. An established aquarium has benificial bacterial, microorganisms, etc. As iamntbatman stated, as long as you are not overstocked, weekly water changes should keep everything under control. I have 4 low-bioload aquariums that I do weekly 20% water changes on. I have had them for years and have never seen nitrate over 10 ppm, with the numbers hardly ever exceeding 7 ppm. In my honest opinion chemicals are not the answer, and neither are full water changes, which will give you a lot more to worry about than nitrates as ammonia builds up extremely quickly in uncycled tanks.

Mikaila31 05-22-2010 12:41 PM

Really depends on your tank and what you are running. 100% WC are fine IF the tank can handle them. You can cause problems if you do a 100% water change on a tank that normally sees 20% water changes. On the other hand many discus breeders will do 100% water changes daily.

In the end though if you are not keeping very sensitive fish or raising fry then nitrates don't really matter.

Byron 05-22-2010 03:11 PM

Previous posts have comments with which I generally agree, but a couple things pop out on which I would like to comment.

Water changes do not affect the nitrification bacteria (cycle, cycling). The bacteria colonize all surfaces covered by water, and removing all the water and replacing it is not going to significantly affect the bacteria. There will always be sufficient nitrosomonas to handle the ammonia produced by the fish and biological processes and they can reproduce quickly even if some may die off when ammonia-heavy water is removed--which I assume was the thinking behind the comment that ammonia builds up quickly with large water changes. I don't believe it does anyway.

If one could manage 100% water changes every day, the fish would love you. This is what they have in nature, water is always flowing past them and they are in "fresh" water (to them) every second. And discus breeders frequently do 90% water changes several times each day in fry tanks, and the discus grow incredibly fast and healthy.

As for the original article, it is another opinion on the subject that should be carefully weighed against the divergent and long-held (by knowledgeable aquarists) views. First, given the link at the bottom, it may have been written by someone connected with the manufacturer of the gadget that removes nitrates and eliminates water changes. Enough said on that. Second, as iamntbatman mentioned, in a properly stocked and balanced aquarium nitrates will not be greater than what the water change can handle. I'm sure those many aquarists on this forum who have non-planted tanks and do weekly water changes and maintain nitrates below 20ppm are proof of this; and in planted tanks nitrates should never be an issue.

I do however believe that nitrates themselves are more of a concern that some may suppose. Most recommendations are to keep nitrate at or below 20ppm, and I suspect there is good reason for this. Some aquarium fish do have issues with nitrates and some with nitrates around 30-40ppm, and there is debate as to how much is tolerable in many fish; no one can dispute that keeping nitrates low is not going to be better than letting them rise without knowing how high is too high for this or that fish. Those elsewhere who advocate doing water changes only when nitrates rise to some "high" level [be it 400ppm or something equally ridiculous] have clearly misunderstood the whole problem.

MrWynO14 05-22-2010 06:13 PM

So, if you have enough plants in a planted tank to keep the nitrate levels down without water changes, how often would the water have to be changed?

Byron 05-22-2010 06:59 PM


Originally Posted by MrWynO14 (Post 389155)
So, if you have enough plants in a planted tank to keep the nitrate levels down without water changes, how often would the water have to be changed?

The need for a partial water change always depends upon the fish load in relation to the water and biological equilibrium. The only reason to do a water change is to remove something "bad" and replace the water with fresh, and this is for the good of the fish. There is more than just nitrates involved in changing the water. There was an excellent 2-part article on this in the November and December 2009 issues of TFH, and a few weeks ago this topic came up somewhere on this forum. I won't get into that now, as you asked specifically on keeping nitrates low, so I'll respond as best I can to that question.

Plants will, if in absolute balance with the fish, handle everything and there is literally never a need to change any water. However, this means a moderate fish load and a high plant load, in a suitably sized volume of water where the balance is able to exist.

Diana Walstad advocates a 50% water change maybe once every six months. Other authors say much the same. I still do 50% every week; but I have a heavy fish load, more than what would be considered a natural balance with the plants. In my 115g the nitrate runs 5-10ppm, whereas in the 90g and 70g it is less than 5ppm; there are considerably more fish per volume in the 115g.

Planted aquaria that are balanced have very low nitrate levels, from zero up to 5 or 10 ppm but very rarely higher. As indicated above, the plant and fish load determines this; the more fish and/or fewer plants, whichever, the higher the nitrate. But it is not at all unusual to have a heavily-planted tank, with a balanced fish load, that never has nitrate reading above zero. This is using the API test kit, which admittedly is not absolute accuracy scientifically speaking, but is sufficient for the purposes of most of us.

The reason is that plants use ammonium/ammonia as their preferred source of nitrogen. Fish and bacteria excrete ammonia as a waste product of their metabolism. In acidic water this automatically changes to ammonium--which is non-toxic to fish [this is how most ammonia detoxifying conditioners work, by changing the ammonia to ammonium]--and the plants grab it fast. In basic water the plants have the capability of using the ammonia in two ways I won't go into here, except to say one is to convert it to ammonium that they then assimilate as their nitrogen. In either case, they tend to out-compete the nitrosomonas bacteria which is why the nitrification cycle in planted tanks is minimal. This means very little nitrite results, which in turn means very little nitrate. And there are some plants that will use the nitrate, though most prefer ammonium because the process within the plant to change the nitrate back to ammonium is more labour-intensive and therefore uses up valuable energy.

Hope this helps to answer your question.


MrWynO14 05-22-2010 10:09 PM

You sure do give a lot of good detail. Here's another thought. If I were to take a hose and start a siphon to take water out of the tank, and at the same time take a hose from my faucet and re-add the water at the same time its siphoning out, would this be a good way to keep an over stocked tank? I'm thinking of letting this run until the water is 100 percent new water, and obviously I would use the same temp of water from the faucet thats in the tank and use dechlorinator.

I don't have an overstocked tank, but I do admit that more fish look more appealing and would like to be able to maintain one. I love american cichlids but they do get very big, and you usually can't keep a whole lot because they are messy fish and produce a lot of waste. Take a look at this tank on youtube, its the same size as mine (135g), and has a lot of cichlids. I'm sure the nitrate load would be pretty high for this amount of bigger sized fish even in this big of a tank, right? It looks good though as far as the health of the fish and has no plants to help with the nitrate load. So would my 2 hose idea work good? I don't want to put my fish in shock or anything, I mean it sounds like a good idea but i need another opinion. Thanx

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