Originally Posted by rsskylight04
I really love the chemistry behind keeping freshwater fishtanks. Thanks guys for such an in-depth treatment of the subject. My interest is mainly academic, and i might just be missing the point but... why get into all this masters level chemistry when stable, healthy conditons can be maintained by regular water changes. I mean, what's so bad about water changes?
I love the idea of an all natural tank with no chemicals or filtration, but in a closed, unnatural system such as an aquarium, it seems pretty obvious that you'll have to remove and replace water regularly to avoid unnatural and unhealthy conditions.
I dont ask this to insult or contradict anyone. I really appreciate the thought and caring that goes into a discussion like this.
Best wishes to all.
Water changes are good. Period. There is absolutely no such thing in this hobby as changing too much water. The chemistry, biology, and ecology behind freshwater systems is absolutely fascinating. Knowing the science behind it is great and does help you predict your tanks surprisingly well. But a lot of it isn't necessary. Chemistry is my career which helps(or cry), biology is my major, I love my many tanks, I also love my kayak and spending time on natural water ways. Needless to say I hardly every test my water beyond pH and TDS. The only reason I bother with those tests is because both are digital pens and really no effort to check once a month. I love that you said closed system, since tanks certainly are. Lakes, rivers, oceans on the other hand are not. Water changes replicate what naturally happens in these systems. The degree is greater due to the incredibly higher bioload aquariums have in comparison.
Flear.... Your still chasing the pot at the end of the rainbow. Plants alone are not going to control TDS. I don't know what natural TDS values are I would assume the range is pretty vast. I've not bother to test for that in my local state. What I can tell you is nitrates usually are not zero(but close), its easy to get and maintain zero in an aquarium due to high favoring of plant growth. Specifically the reason a lot of planted keepers add nitrates is to stop it from hitting zero. Plants do a role in cycling nutrients but they certainly don't do it alone in a natural system. I keep some crazy densely planted tank... I knock the glass on some of them prior to feeding to let the fish know since the plants are seriously that thick. Part of the reason IDK how many fish I have.
Plants will take up some TDS out of the water but its not going to be close to equal the build up. Likewise fish produce hormones the same is true for plants. They also produce a wide range of hormones, all plants do. TDS = total dissolved solids. This includes everything inorganic and organic that is dissolved. You cannot test individually for everything a TDS meter will pick up without spending a small fortune. EVERYTHING contributes to TDS. Your fish food, dechlorinator, that useless pH buffer, that driftwood you added, evaporation, fertilizers, most substrates, ect, ect, and ect. All are going to push TDS upwards.
TDS can fluctuate, everything does, the importance is it doesn't constantly build up. When I dosed all my fertilizer to that tank awhile back with the gypsum, baking soda, mag. sulfate the total sum was 2.5 tsp of powdered solids. In comparison to my neglected tank the TDS in that tank is currently 270ppm. The difference here is I know what is contributing to it. And the tank has large water changes to remove excess which drops the TDS before redosing. This is the same tank I use to breed GBR on an almost weekly basis for many months. This
is a simplified
carbon cycle in a natural lake. First thing to note there is surface water input and groundwater input. There is also surface water output! Its still not a closed cycle! As Austin mentioned organics are certainly soluble. Alcohol mixes with water and it would be a tragedy if it didn't, since I don't sober post here anymore. DOC= dissolved organic compounds and is an important factor in aquatic systems. POC= partial organic compounds which are suspended but not dissolved, usually because they are not fully broken down by bacteria and fungi. Simple example of this is wood secretes tannic acids(along with much more) this is an organic compound and it will hang around for a long time before it eventually gets broken down (also will factor into the 'unaccounted' on a TDS meter). Trees fall into lakes introduce a easy ton or more of wood which will eventually get broken down by the lake. There are whole trophic levels missing in an aquarium that play a role here. Fish are one of the highest trophic levels in an aquatic system and thus have the smallest bioload and are of the least importance. Lakes and rivers all over the world play a huge role for insect larva. You really don't wanna know how many insects a square mile of lake can produce. Many of which leave the lake as winged adults, fly off, a huge amount of them get eaten by birds, bats, and other organisms. Again this is an output of nutrients leaving the lake. Its not closed, it never has been, and your gonna need to learn magic to make it so.
Soft and hard is determined by gH and kH and IDK the ranges off the top of my head. TDS varies since again its a sum of everything which at the same time tells you nothing of whats what. The 'typical' dose of salt for FW will shoot your TDS up 300-400ppm in my experience. I would say for FW system TDS is typically below 500ppm unless you are counting the rift lakes. But say adding salt to my tap water and expecting it to be anything like the rift lakes based on TDS is gonna get you nowhere fast.
Flear you could spend years on trying to make a self sufficient tank and still its not gonna happen. Designing a low maintenance tank with a high output isn't that hard. And it will pay you back before you figure out how to make a self sustaining one. Just my advice. Physics dictate chemistry, which dictates biology, which dictates ecology.
Originally Posted by beaslbob
that does not seem to be obvious at all to me. Unless you do massive water changes frequently, waer changes will never maintain healthy conditions by themselves. What will happens is conditions build up to where the conditions just before a water change equals the change between water changes divided by the fraction of water change. so if you change 1/5 of the water the tank conditions will be 5 times the change between water changes. Plus whatever is in the replacement water. So unless you are doing 100% daiily water changes with perfect water, the tank conditions override the water change effect.
So what is important is to limit the amount the tank changes. then the water changes are irrelevant and in fact can only deteriorate conditions.
Hence I have kept FW and marine tanks for up to 9 years with no water changes.
A tank will actually maintain levels with regular water changes, and always the more the better. The fact is things do level off like you mentioned. As levels increase while a tank establishes you eventually hit a point where levels in the tank become concentrated enough that the water changes remove an amount equal to the build up and thing stay basically stable. The math isn't as straight forward as that. The catch to this is the less water you change the higher the levels become before they stabilize and hold there. Which again comes down to more water changed is better. So you are correct the less and longer between changes the more conditions change. If you want a tank to stay similar to your tap water try 50% or more change a week. The reason keeping a high tech planted tank(or simply high demand) and dosing heavy fertilizers requires 50% weekly changes is again to ensure nothing builds up excessively.