Why do i need to change the water?

Discussion in 'Water Chemistry' started by Skatersav, 16 Dec 2011.

  1. Skatersav

    Skatersav Member

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    I realise that this may sound like a stupid question, but I would like to explore the issue of water changes a bit to try and understand the chemistry of what is happening in my tank.

    So, as background, I run a 350litre planted tank (pressurised CO2 with inline difuser, 2 big Eheim filters rated at around 900litres per hour (or something) and a couple of big pumps for water circulation, RO water, lots of plants with attractive latin names, a small school of Denison barbs and some of those long silvery fish with the black line that are famously partial to hair algae (Siamese flying foxes or something??)). I've been in the process of immersing myself in the world of planted tanks over the past year and learning as I go with some muted success - I am yet to grow any of the fabled HC, but I think I have successfully conquered algae (although, in response to this brazenly arrogant claim, my tank is probably furring up with toxic green sludge as I write this). I typically change about 20% per week, which is actually quite a hassle given the amount of RO water I need to produce and I have a nagging concern about how much perfectly usable water the RO machine must be discharging. I live in London where the water apparently passes through 7 people between source and the sea, so I am reluctant to use any tap water in my aquarium. I recognise that passing through a human gut doesn't necessarily render water unusable but, nevertheless, I have had trouble keeping fish in the stuff before. So, I am left in a situation where I truly loathe making water changes.

    Anyway, I was recently enlightened on the subject of nitrates and phosphates by the wise Greg of the Aquatic Design Centre. In response to his teachings, I have been targeting the desired 10:1 ratio and have found that even without any additional EI fertilisers my tank seems to be fairly steady at something approximately within that range. Arguably both could be lower, but if I don't add any minerals, both seem stable over time. Indeed, this week I have not made any water change and both have been pretty steady. Nitrates are probably slightly higher than 12.5mg/l and Phosphates are probably around 1.5mg/l. I am reluctant to place too much faith in the exactness of any of these home test kits: telling whether the water contains 25mg/l of nitrate or 12.5g/l is like trying to explain to your 3 year old son the difference between a mandarin and satsuma.

    So, this leads me to my questions: why do I need to do any water change at all if the aim is to keep nitrates and phosphates at a safe level, and both seem to be stable at safe levels anyway? If I keep my plants growing strongly with good light and good CO2, add the necessary micro nutrients and prune regularly, is there any need to change the water? What else can be building up in the tank that I don't know about that might need diluted with fresh water? And, finally, if I don't add the macro nutrients in my EI kit am I failing to add some other magic ingredient needed to fend off algae and keep my plants growing?

    Of course, should I increase the bioload then I'm sure the current stable condition will degenerate, so all of the above is founded on the supposition that my nitrate and phosphate levels remain at a safe level and the correct ratio.

    Any help would be appreciated and thanks in advance. I fully intend to upload some pictures of my tank as soon as I can capture an image with the barbs sitting vaguely still: they constantly charge about the place and so every photo is covered in these little red streaks. Actually, I note that there is not a tutorial on photography on this site... I would love to contribute myself: maybe one day I will be wise enough to do so.
     
  2. George Farmer

    George Farmer Founder Staff Member

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    Hi there

    The water changes in a high-energy system like yours are to dilute waste organic matter produced by both fish and plants.

    These waste products tend to trigger algae, so by diluting them via large water changes minimises the risk of algae.

    As you know, dosing inorganic N and P via ferts will not cause algae in a healthy planted tank, but organic N and P build-up as a consequence of lack of maintenance may cause algae.

    This is why it's a bad idea to simply add more fish to increase N and P levels. More fish means more organic ammonia, which is said to be a huge algae trigger.

    Interestingly N in ferts comes in the form of ammonia nitrate, but shouldn't trigger algae. I presume because it's inorganic and that the plants love it!

    Generally speaking the more water changes the better in higher energy planted tank system with good light, CO2, nutrients, circulation etc. I always aim to change at least 50% per week in most of my set-ups. Perhaps once every 2 weeks in larger aquariums because I'm a bit lazy.

    Cheers,
    George
     
  3. Skatersav

    Skatersav Member

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    Thanks George. I didn't realise the plant life/algae distinguished between inorganic and organic sources of N and P. I suppose this means that I need to maintain the 10:1 ratio of nitrate to phosphate but do so via big water changes and dosing of fertilisers rather than by simply allowing the organic processes to build up these nutrients. That's very helpful.
     
  4. Piece-of-fish

    Piece-of-fish Member

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    You also dilute any potential build up of ferts especially if dosing EI heavily.
     
  5. foxfish

    foxfish Member

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  6. Skatersav

    Skatersav Member

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    Thanks. It's interesting actually. Even though the nitrate and phosphate levels remain within acceptable levels, I'm sure I am starting to see spots of algae popping up on some of the plants. I'm going to start EI in earnest with a much larger water change. Going to start mixing in some tap water as well because I reckon it should be ok when diluted with the RO water. Thanks all for your contributions.
     
  7. Matt Warner

    Matt Warner Member

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    Hi skatersav. I don't know why you don't just use 100% tap water. What is it that makes London water so bad. I know that it can have a very high ph, but I would just buy fish to suit the high ph such as guppys or platys. Unless the tap water contains ammonia or nitrite, I would use it. Dechlorinator will take care of high levels of chlorine and chloramine. Just think of the money and hassle you will save yourself!
     
  8. Skatersav

    Skatersav Member

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    Matty, I don't know what it is in London water that has nailed my fish in the past, but there is definitely something going on. I'm also toying with the ideas of discus... You're right though. I'm going to switch to much larger water changes, lots of ei stuff, and I'll start cutting my ro water with 50% tap water. Cheers all. S
     
  9. plantbrain

    plantbrain Expert

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    Outside of nutrient management, I do notice whatever level I drain the water to, the level above that is always algae free on the glass in every aquarium. In moist, there's no algae either way.

    But if I uproot plants, scrape or scrub off algae, trim heavy one day, leaves everywhere, made a big mess etc, any detritus laying around, tannins, off color in the water, want to whip the tank into shape etc........water changes have never hurt, but these things have NOTHING to do with fert management.

    They do have a lot to do with horticulture and good aquarium care, craftsmanship.

    If low input is the goal, then non CO2 offers a good low intensity planted tank that can look very nice.......

    Note, you can still do discus in a non CO2 method and do VERY well.
    Imagine this 60p ADA tank that has a wet/dry, but at a 180 cm scale with 8 nice full sized discus, Cory sterbai and some nice red pencil fish.

    ca09afe4.jpg

    Since much of the plant growth is on top, algae free............and plenty of CO2, and makes a nice cover for the fish.

    You might gravel vac once a month maybe 10-20% of the water in such a system with Frozen Blood worn feeding.
     
  10. Tim Harrison

    Tim Harrison Super Moderator Staff Member

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    I am intrigued to learn that both higher and lower plants can distinguish between so called inorganic and organic compounds of the same elements, and that accordingly regular water changes can keep algal blooms under control.

    I would also be very intrigued to know why this is, and what the biochemical processes behind this theory are?

    A firm understanding of the processes involved would benefit us all.
     
  11. plantbrain

    plantbrain Expert

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    Troi, if we consider the idea as a type of "competition" for those limiting nutrients, whether plant, bacteria or algae.......then if I can get at the resource before it's broken down by bacteria into inorganic compoents, I would have an advantage in limiting systems.

    But...in non limiting system, eg, where there is little competition.......then there is no advantage.
    What else does organic waste entail? Well, sewer treatment plants add O2, or use trickle filters etc, to help go from organic waste(bacteria need to break this down to NH4, which requires huge amounts of O2, then NH4 to NO3, which also requires lots of O2).

    Perhaps algae spores detect these changes in O2 and bacteria, perhaps plants do as well.

    Periphyton that normally grows on nice healthy growing plants........may change when the O2, and waste loading change, rather than the plants directly themselves, then the periphyton goes from a healthy intact system(much like a Tropical rainforest, not much exotic invasive weeds in those locations) to a disturbed system where algae spores can land and germinate easily. This is just one hypothesis and speculation.

    We really do not know that much about why algae grows and does not grow in a planted tank, we can induce things, but these tend to be things that stress the plant.

    So poor plant health = algae growth/germination.

    But, we are horticulturalist.......so our focus is really growing the plants, not avoiding algae directly.
    What we like as far as management is CONTROL of those rates of growth, less = easier, more = more gardening and labor.

    These are different horticultural goals.
    We can not suggest that the methods will be the same with such differing goals, no one method will meet all goals, this is not a satisfactory assumption. So we need different methods for each goal set and look at the trade offs they impose.

    We can look at different systems and see we have a higher % of organic loading for the nutrients is say a non CO2 system with good fish loads.

    Then consider a CO2 enriched system(same light) with virtually no fish/livestock and inorganic nutrients.

    Growth will occur in both tanks, but one will have a wider range of inputs/outputs and another will reply more of the fish linkage. Which of these 2 systems could go wrong if you over did things? Which would have the higher O2/bacterial loading linkage??

    I think one thing to really consider is a lack of algae eaters in many non CO2 systems, this would help a great deal I believe. Since plant growth is slower, and so is algae growth, each critter has more time to gnaw at algae.

    So you get more work out of them.

    Soil cycling with these same thing sis another process separate from the water column often times.
    If you like soil(I know you do), Reddy and LaRue 's text on Biogeochemical cycling of wetland soils is a excellent reference text for anyone interested in this topic. Not cheap but filled with 101 good articles and support.
    Reddy was my old Grad soils prof, smart guy.

    "Sigee"'s Freshwater microbiology also might be of use.

    You might find them used for sale.
     

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