i do my pwc's with 5 gallon buckets. i was wondering if i can take 5 gallons out and then put 5 gallons of clean water in. and repeat the process.
the reason i want to do it like this is because when my water level gets too low and i start to dump water back in i stir up a bunch of debris and some of my plants (baby tears) uproot no matter how carefull i am
now if i can do it like that i'm assuming i would have to change more water, right?
I used an excel spreadsheet to figure this out for my own purposes. HERE is the answer to your question.
When using 5 gallon buckets, I used a 1 gal milk container to mark lines for each gallon. A 5g bucket has to be full to within 1/2" of the top to actually contain 5 gallons. Since this is a b@#ch to lift up to the edge, typically I don't fill to more than 4 gallons, but here's how it works if you actually siphon out 5 gallons and put back in 5 gallons. This is assuming that you have effectively 50 gallons of water and 5 gallons worth of substrate and other materials displacing that volume of water
After first 5 gallon change:
45 gallons original
5 gallons new (10% change)
After second change:
40.5 gallons original
9.5 new (19% change)
After third change:
36.45 g original
13.55 g new (27.1% change)
Fourth
32.81 original
17.2 new (34.4% change)
Fifth
29.52 original
20.48 new (41%)
Sixth
26.57 original
23.43 new (46.9%)
Seventh
23.91 original
26.09 new (52.2%)
Each time you have to figure out your new gallons/old gallons, then if you take 5 out, you have taken out proportionally the same amount of old/new water.
Hope this answers your question
If you do 4 gallons at a time your percentages work like this:
1: 8%
2: 15.4%
3: 22.1%
4: 28.4%
5: 34.1%
6: 39.4%
7: 44.2%
8: 48.7%
9: 52.8%
I don't use a python because I can't justify $90 for it, or even $40 for the cheaper version with less hose. Just a regular gravel vac, $10-15. Plus the fact that how are you supposed to dechlorinate and detoxify your water before dumping it into the tank with a python, by IV drip? Ok for removing water, not so much for adding IMHO, but many other swear by them.
As for me, I do 2 4.5g buckets worth every other day, 3g goes into my 10g and the other 6 in the 55, if you add that up using the above calculation method, I am effectively changing between 30 and 40% of the water in my 55g every week, and no need for sucking out 20 gallons at once each week.
Of course, my municipal water sucks bad, so it's not really that safe to do major water changes on my tanks unless it's completely necessary.