Adding water to existing tank?

[russrimm]

Our tanks get down an inch or two in water every week or so from normal evaporation. I've heard that it's not a good idea to just keep topping off the water as it goes down, as you'll increase the water hardness over and over. Is this true, and if so, should we just do a 20-30% water change instead of topping it off? Do you do 20-30% from the current water level, or 20-30% of full?

 

[Jchillin]

You can top off an inch or two without a problem. That is unless you have elements in your tap water. In which case the top off water should be treated prior to using it. PWC's should only be done according to your schedule. If it coincides with the evaporation schedule, you can do your normal PWC and that elements adding water.

 

[russrimm]

Which elements are you referring to and how do I test for them? A GH test kit?

 

[Jchillin]

I assume the water in your tank came from your tap. If so, you should have tested the ph (acidity/alkalinity) of your water already. Hard water refers to water that contains higher levels of minerals. Usually municipal water doesn't contain this but it doesn't hurt to find out.

 

[russrimm]

So if I have municipal water, its probably safe to just top off the water if it's 1-2" down? Can I do this over and over again until I do my PWC?

 

[hashbaz]

I've heard that it's not a good idea to just keep topping off the water as it goes down, as you'll increase the water hardness over and over. Is this true, and if so, should we just do a 20-30% water change instead of topping it off? Do you do 20-30% from the current water level, or 20-30% of full?

You are correct - your hardness will increase over time. But just doing water changes will not solve the problem.

If you have time for a detailed (and boring) explanation, here goes. Hardness is a measure of the amount of minerals (calcium, magnesium, carbonates etc.) dissolved in your water. These are naturally in your tap water. Some place have more and some places have less.

1st Think of your aquarium in terms of what goes in and what goes out. In evaporation water goes out and minerals stay behind - this increases hardness. When you siphon water out both water and minerals leave your tank - and the hardness stays the same.

Adding tap water can change the hardness of your tank water. If the tap water is softer, your tank will get a little softer. If the tap water is harder, your tank water will get a little harder. Normally your tap water will be softer than your tank unless you use distilled or RO water.

As to your question about water changes. Changing more water (more often and/or in larger amounts) will keep your water softer. This is because your aquarium will eventually reach a balance. When this happens, the water and minerals leaving each week will be replaced by the same amount of water and minerals. If you add only tap water each week, the hardness of your tank water will increase until the concentration of minerals in your water is high enough that the minerals siphoned out each week are the same as the minerals added each week.

All this boils down to 2 things:

1. If you want your tank water hardness to exactly match your tap water hardness, you need to replace the amount of water lost to evaporation with the same amount of pure water (distilled or RO). Exactly when you do this will not matter. I choose to do it after/during the water change.

2. When using only tap water, the hardness of your tank water will increase to a certain amount, which is set by the amount of your water changes:
- more water changes = softer tank water (closer to tap water hardness)
- less water changes = harder water

How hard is your tap water? How hard is your tank water? And how hard to you want your tank water?

 

[Jchillin]

In which case the top off water should be treated prior to using it. PWC's should only be done according to your schedule. If it coincides with the evaporation schedule, you can do your normal PWC and that elements adding water.

Russ - This is the most important part. If you have hard water, treat it before adding. If you wait until you do a PWC, problem solved. What is your current PWC schedule?

 

[Concubine]

it is o.k. if you just top off the water but it needs to be treated first,but i would just wait to do it when you do your water change(s)

 

[russrimm]

When you say treated, do you mean the chlorine/chloramine removers? I always pour some in when I do a PWC. I don't know how hard my water is, I guess I should test it. That GH test is kinda confusing I noticed too.