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With EI dosing you do one weekly 50% water change.

What it make a big difference, if at all, to do three smaller water changes? So on a 29g if I did three 5g changes.

I would probably do it on Monday, Thursday, and Saturday.

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You'd have to change proportionally more water, since at each water change you're changing a blend of the old water and the water from the last change.

I won't do the math because it's Friday, but someone could.

#### Raymond S.

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Long story short two 10g water changes don't do the same thing in your tank as one 20g water change does. You need to increase the amounts in the 10g water changes.
Not my thing so I just stick to the recommended WC of 50% once a week.

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From: Drip System Water Change Rate Calculator (W.C.S. Ltd.)

Tank Volume 29 Gallons

Water Dripped in per Day 5 Gallons

The drip system will change 15.84 % of the Tank's water in one day and 29.17 % in two days.

Assuming no additional pollutants are added, drip system will replace 70.09 % of the Tank's water in a week.

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Long story short two 10g water changes don't do the same thing in your tank as one 20g water change does. You need to increase the amounts in the 10g water changes.
Not my thing so I just stick to the recommended WC of 50% once a week.
So I would probably need like daily 5g changes?

From: Drip System Water Change Rate Calculator (W.C.S. Ltd.)

Tank Volume 29 Gallons

Water Dripped in per Day 5 Gallons

The drip system will change 15.84 % of the Tank's water in one day and 29.17 % in two days.

Assuming no additional pollutants are added, drip system will replace 70.09 % of the Tank's water in a week.
That is very interesting, I may have to look into getting a drop system. Thanks!

You'd have to change proportionally more water, since at each water change you're changing a blend of the old water and the water from the last change.

I won't do the math because it's Friday, but someone could.
OK thanks, I'll try to find a calculator to get an exact amount. I never thought about it that way.

According to https://www.hamzasreef.com/Contents/Calculators/EffectiveWaterChange.php

If I do two 10g changes over a 6 day span it would change 57%. Is that right or am I missing something?

#### Savetheplants

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In a 29 gallon tank assuming 15% for displacement you would need to do three 5 gallon 1 pint water changes to change approximately 50% of your water in a week. Let x = percentage of water after adjusting for displacement left in the tank each water change. x^3=0.5. Subtract 1 from x and change the sign. Multiply the difference by displacement adjusted volume of water in the tank to get volume of water needed for each water change.

#### theatermusic87

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Using zorfox's calculator for dosing accumulation you end up with basically the same ppm over time in the water either way. This is assuming 50% every 7 days vs 20% every other day.

Using the same software if you change ~20% of your water every other day (5 gallons) you will have effectively changed 45% of your water every week... so in the grand scheme of things it makes no difference

The only thing i noticed is looking at the graph that the concentration of what ever you are dosing was much more stable with a 3x 20% water change than a 50%.. i.e. it didn't swing up and down as much over the course of the week... better or worse I have no idea, but it is worth noting

If you'd like to play around with the numbers yourself this is the software they're a forum member as well if you have questions

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Using zorfox's calculator for dosing accumulation you end up with basically the same ppm over time in the water either way. This is assuming 50% every 7 days vs 20% every other day.

Using the same software if you change ~20% of your water every other day (5 gallons) you will have effectively changed 45% of your water every week... so in the grand scheme of things it makes no difference

The only thing i noticed is looking at the graph that the concentration of what ever you are dosing was much more stable with a 3x 20% water change than a 50%.. i.e. it didn't swing up and down as much over the course of the week... better or worse I have no idea, but it is worth noting

If you'd like to play around with the numbers yourself this is the software they're a forum member as well if you have questions
Hmmm that's an interesting point. I wonder if having more stable nutrients in the tank is better than large swings. Three 5g changes is only 5% less water than one 14.5g
change. So it's very similar. Certainly a lot easier for me to do and less stressful on the fish.

Has this not been brought up much before because there is an issue that has not yet been brought up or because most find it easier to do one 50% change?

Either way, it's a good discussion

#### Diana

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I would have guessed 3 x 20% to 25% in one week might come close to 1 x 50%.
Using Zorfox' calculator for nutrient accumulation over several water change scenarios is a good way to figure this out.

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