Question about topping off

[sparkymcjay]

Well, some water has evaporated from my tank and im going to top off and do a water change tomorrow. I have some RO water, but I need to know what do I do to get the ph the same as my aquarium, or if I should just add it as is? I think I read somewhere to use baking soda, will that work? Thanks for any help.

 

[Maxi]

When water evaporates, just add RO/DI water. Do not add saltwater. The salt in the water doesn't evaporate in the tank, but the water does.

 

[sparkymcjay]

I know that not to add saltwater for a top off, im asking what do i need to add to the RO water to match ph before i add it to my aquarium? Or can I just add the RO water as is?

 

[StephenInVa]

Lots of people allow the water to sit over night with some sort of aeration device or pump in it. This lets the pH stabilize to around 7.0 (in my experience anyway) and get an oxygen saturation. You however don't have to do either if you don't want. Besides it'd be a pain getting the freshwater you're using for top off to a high enough pH to match your saltwater. I take the water from my collection barrel and mix kalk into it then drip it into my tanks sumps. You'd be fine just slowly pouring it into the sump if you're not dosing kalk however. If it's a smaller tank and you don't have a sump I'd place the water container above the tank and use a piece of airline tubing to siphon it into the tank. Make sure the water enters in a high flow area so it's mixed up. The amount used for top off shouldn't affect your pH or salinity enough to cause any harm. Unless you're waiting a long time to add top off water.

 

[sparkymcjay]

Its not a lot of water missing im just being cautious cause I thought that if I added water with a ph lower then that of my aquarium it might mess something up. Thanks again.

 

[tuckrule]

I bet you 99 percent of salt water aquarists, justt add plain old RO/DI water when topping off. NOt adding anything to it. Including myself.

 

[otrlynn]

<a href=showthread.php?s=&postid=13216388#post13216388 target=_blank>Originally posted</a> by tuckrule
I bet you 99 percent of salt water aquarists, justt add plain old RO/DI water when topping off. NOt adding anything to it. Including myself.

I'm one of the 99%. I don't have a sump and I just slowly pour the water into the tank, right over a powerhead where it is dispersed immediately. I don't aerate the water before using it. I generally do 10% water changes and don't even worry too much about the temp of the water. The exception is in the middle of the winter; we keep our house on the cool side, and I put a small heater in the top off bucket overnight.

 

[crvz]

agreed with tuckrule, there is no need to equalize pH in top off water before adding it. you'll be fine.

 

[1fishkeeper]

Dido on that. I have my line from my RO unit going right into my sump.

 

[Michael]

forget trying to equalise ph, just top off with the ro, litrally thats it, as for baking soda, when you have lots of corals your alkiliniy may drop quite quickly and when you top off you can add the baking soda to raise the alk, id monitor your alk first though and never dose anything unless you have been testing for it ok, good luck and get that ro top off water in there

 

[d0ughb0y]

ph of the ro di water should be neutral, at around 7. I am guessing the water that evaporated has a ph of around 7 also, so in theory if you try to increase the ph of your top off water, you are actually going to alter the ph of your tank. for the same reason the evaporated water sg is going to be 1.0, so you replace with water with 1.0 sg.

 

[Randy Holmes-Farley]

It is fine to use RO/DI water to deliver things that you need in the tank, but it is neither necessary nor desirable to match the pH of the RO/DI to the tank. I discuss that here:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm


from it:

http://www.reefkeeping.com/issues/2005-05/rhf/index.php#8

Final Effluent pH

Aside from the issues discussed above concerning the effluent’s pH when the DI resin becomes depleted, the final pH coming out of an RO/DI system should not significantly concern reef aquarists. Many aquarists with low pH problems have asked, for example, if their aquarium’s low pH may be caused by their replacing evaporated water with RO/DI water that they measure to have a pH below 7. In short, the answer is no, this is not a cause of low pH nor is it something to be generally concerned about, for the following reasons:

1. The pH of totally pure water is around 7 (with the exact value depending on temperature). As carbon dioxide from the atmosphere enters the water, the pH drops into the 6’s and even into the 5’s, depending on the amount of CO2. At saturation with the level of CO2 in normal (outside) air, the pH would be about 5.66. Indoor air often has even more CO2, and the pH can drop a bit lower, into the 5’s. Consequently, the pH of highly purified water coming from an RO/DI unit is expected to be in the pH 5-7 range.

2. The pH of highly purified water is not accurately measured by test kits, or by pH meters. There are several different reasons for this, including the fact that highly purified water has very little buffering capacity, so its pH is easily changed. Even the acidity or basicity of a pH test kit’s indicator dye is enough to alter pure water’s measured pH. As for pH meters, the probes themselves do not function well in the very low ionic strength of pure freshwater, and trace impurities on them can swing the pH around quite a bit.

3. The pH of the combination of two solutions does not necessarily reflect the average (not even a weighted average) of their two pH values. The final pH of a mixture may actually not even be between the pH’s of the two solutions when combined. Consequently, adding pH 7 pure water to pH 8.2 seawater may not even result in a pH below 8.2, but rather might be higher than 8.2 (for complex reasons relating to the acidity of bicarbonate in seawater vs. freshwater).