Aquarium & Tropical Fish Site

This repository is for research only. New discussions take place in our current Tropical Fish Forum.

Archivarium 2004
Repository of our 2003/2004 Topics
 
  HelpHelp   Search BoardSearch Board   MemberlistMemberlist   UsergroupsUsergroups 
 ProfileProfile   Check your private messagesCheck your private messages   Log inLog in   RegisterRegister 
Ideal Water Change Regime
 Forum Index > Marine Equipment and Chemistry  Search Board
View previous topic :: View next topic  
Author Message
The Kapenta Kid
Regulars


Joined: 02 Mar 2004
Location: Brussels, Belgium

PostPosted: 2004.04.06(Tue)9:25    Post subject: Ideal Water Change Regime Reply with quote

What would be the ideal frequency and volume of regular water changes for a stable, heavily planted, community freshwater tank?
I am talking about tanks in the range of say 30 to 90 gallons and where there is little or no substrate exposed for regular gravel vaccing combined with the water changes. Also where the tap water chemistry is similar to the tank chemistry.
(In my case pH 7, GH 18, KH 10 German scale and DIY CO2 injection. My tap water is also 20-25 ppm nitrates which is lucky since my plants suck the tank nitrates down to a critical 5 ppm in about a week. After a 25% water change this goes up to 10-15 ppm. Nitrites and ammonia are of course 0.)
Presumably, and this is only my assumption, very frequent, very high volume changes (say 75% or more) are stressful to the fish and also dilute plant nutrients.
But taking 25% a week as a base, how frequently and how high could you go before you hit the point of diminishing returns.
To save anyone making the obvious point, I am ignoring the labor involved.
_________________
Men live like fishes;
the great ones devour the small
Back to top
View user's profile Send private message
anonapersona
Advisors


Joined: 06 Feb 2003
Location: Houston, Texas

PostPosted: 2004.04.06(Tue)17:43    Post subject: 5-10 ppm nitrates consumption Reply with quote

I think the key for you will be the nitrate consumption, as you already see. Here in our area where nitrates in the water are 0, I use water changes to dillute "invisible fish wastes" and to dillute any potential overdose of the fertilizers I am adding. So, my weekly 50% water chnges limit the potential for buildup of excess fertilizers to twice the level at which I add them. (If I add something and it is not consumed, half of it is removed at the next water change and I add more... it eventually approaches twice the added concentration)

In you case you are using it to add fertilizers and to dillute fish wastes. Do you also have high phosphate levels? Whichever of these are the higher will be the controlling function for your water changes I'd think.

If you did larger and/or more frequent water changes, you'd be approaching that 25ppm of nitrates of the tap water that a 100% water change would produce. You said that your tank can consume 5 to 10 ppm of nitrate in a week. You, therefore do not want to add more than 10 ppm to the tank a week or it will begin to build up. Building up to 25ppm is not dangerous, however, so you could do that if you wanted, if the phosphate level was not an issue.

There is no reason to assume that high and/or frequent changes are bad for the fish. Your tap water is similar to the tank, water changes keep it that way. The more it changes, the more it stays the same! Yes, you will dillute the plant nutrients that you are adding that are not contained in the tap water, whatever those are. If you are using expensive additives, that is an issue to consider.

As far as diminsihing returns, hmm... let's look at 25% per week, you say that gets you 15ppm falling to 5ppm by the end of the week. Pretty good. That means that the tap is actually 45ppm nitrates... .75x5ppm + .25x45ppm = 15ppm, but that is pretty far from what you thought you had. Maybe the error is in the other end... .75x0 + .25x20 = 5ppm... still pretty far from what you thought you had, it is not likely to mistake 0ppm for 5ppm.

I'm going to guess that the tap is much higher than you thought.

Now a 100% water changes will give you 45ppm, rather high, so you don't want that, but at your rate of consumption that will take you 4 weeks to run down to 5ppm.

75% will get you .75x45 + .25x5 = 35ppm, still too high, IMO, but 3 weeks to get to 5ppm. If you did this weekly your nitrates would be rising, at thend of the first week it would be 25ppm, then with a water change .75x45 +.25x25 = 40ppm, next week .75x45 + .25x40 = 43.75, and it continues to approach the tap water levels rapidly.

50% will get .5x45 + .5x5 = 25 ppm, OK but still pretty high, but you could run two weeks between water changes to get to 5ppm again if the tank consumes 10 ppm per week. That might be nice. If you do this weekly, it approaches tap levels, but more slowly.

Are you adding anything that would be building up to bad levels if it were not consumed in two weeks?

On to 25% weekly .25x45 + .75x5 = 15ppm, ideal IMO, based on the numbers you gave us.

Now, you could do smaller changes more often, for the square root of .75 is .86 so two 15% water changes in the week are just like one 25% change. More work, same result.

If you begin when the tank is at 5ppm, 15% is .15x45 + .85x5 = 11, and the tank consumes 5ppm in a helf week so at next biweekly change you are at 6 instead of 5...the start of a buildup.

So, for your needs, with the tap containing your fertilizer, you are dosing the tank with tap water as well as dilluting the tank wastes. I think you want to stay on a weekly or bi-monthly water change routine to be sure waste is removed, but you have to limit how much tap you add to avoid getting the nitrates too high. I'd suggest changing water when the nitrates got to 5ppm, then basing your volume on how long you want to go to the next change.
Back to top
View user's profile Send private message
The Kapenta Kid
Regulars


Joined: 02 Mar 2004
Location: Brussels, Belgium

PostPosted: 2004.04.06(Tue)18:30    Post subject: Reply with quote

Thanks for your very detailed response.
You are probably correct in assuming that my nitrate levels are higher than I seem to test. I distrust the absolute levels that nitrate test kits give (I'm in Europe and I use the JBL nitrate tests which I prefer to Tetra) although the relative readings are probably OK.
My tank water phosphate readings are also high, 1.5 ppm dropping to 1 ppm after a water change. My tap water phosphate is zippo so I attribute the tank levels to over feeding, I'm a relative newbie so I haven't got the kindness/correctness balance right yet.
_________________
Men live like fishes;
the great ones devour the small
Back to top
View user's profile Send private message
anonapersona
Advisors


Joined: 06 Feb 2003
Location: Houston, Texas

PostPosted: 2004.04.07(Wed)16:40    Post subject: eyeballing the food to feed Reply with quote

I've been told that you should feed each fish the amount of food equivalent to it's eyeball. Once a day, and it is OK to skip a day routinely. It is also OK to not feed for several days. With a well planted tank it is OK to not feed for a week or two.

I will mention that in my big cichlid tank, fish only, if I don't feed them they start to fight amongst themselves. The planted fishtanks with tetras and other small well-behaved fish don't have this problem.
Back to top
View user's profile Send private message
The Kapenta Kid
Regulars


Joined: 02 Mar 2004
Location: Brussels, Belgium

PostPosted: 2004.04.07(Wed)17:38    Post subject: Reply with quote

uuh... Anonapersona, I think you have posted to the wrong thread
_________________
Men live like fishes;
the great ones devour the small
Back to top
View user's profile Send private message
anonapersona
Advisors


Joined: 06 Feb 2003
Location: Houston, Texas

PostPosted: 2004.04.08(Thu)7:41    Post subject: oops! Reply with quote

The Kapenta Kid wrote:
uuh... Anonapersona, I think you have posted to the wrong thread


Now, how did THAT happen!

anona, who only had ONE glass of wine, I swear!
Back to top
View user's profile Send private message
Display posts from previous:   
 Forum Index > Marine Equipment and Chemistry All times are GMT - 6 Hours Search Board
Jump to:  
  You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2008 phpBB Group

oF <=> oC in <=> cm G <=> L