Evaporation and Distilled Water

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fishorama

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Jun 28, 2006
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I'm going to need a day or 3 to digest all this info but it's good info...I may have questions but I'm not ready yet (massaging my head to get a grip isn't working so far). Others are probably quicker on the uptake...
 

tackful

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Mar 15, 2007
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Perhaps there is an easier way to show this. With the same hypothetical example, imagine:

1) 11 gal worth of TDS in our 10 gal tank
2) After 1 gal evaporates, we now have the same 11 gal of TDS in only 9 gal of tank water
3) We remove 50% of the tank water, now leaving 5 1/2 gal of TDS in only 4 1/2 gal of tank water
4) Finally ,we add back 5 1/2 gal of treated tap water, restoring our TDS to 11 gal worth and our tank to 10 gal, bringing us back to our original concentration.
 

fishorama

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OK that makes sense, but so did your previous math...after a while (ahem :rolleyes: ). Dilution math can get tricky because it's not exact & then it gets more iffy over time.

This is why a TDS meter helps in the long & even short term. There can be dissolved solids that are slowly increasing (from ferts or rocks, whatever)...& try as we may we don't ever feed, WC or apply ferts the exact same amount. & then there's seasonal water issues. I'm in CA too, I know!

Just spend $13 next time you order from Amazon to get a TDS meter. I guarantee that it will be easier & more exact to your tank than trying to figure water dilution by math possibilities alone...I miss my TDS (It's almost a song...I miss my MTV...I think you know ;))

Do the best you can with WCs but if you really want to know you need a TDS meter...even a cheap 1 helps.
 

Rbishop

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You keep mentioning things like " 11 gallons of TDS in a 10 gallon tank. That is not accurate at all. TDS is a value basically of conductivity. Unless you are measuring before and after, of the tank AND the replacement water, you can't accurately do the math. Also, your substrate and decor effect the actual volume of the tank. There are many sources on line that can show you the computations. And, treated tap water has a different TDS than plain tap water. I believe you are over thinking the whole issue.
 

dougall

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Mar 29, 2005
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Do you work out how much ammonia is in the tank in a similar manner?

There are too many variables to increase and decrease dissolved solids in the water, just test. You are also relying on the TDS of your source water being constant.. which it will not be.

🤷
 

tackful

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Mar 15, 2007
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TDS meter arrived last week. Reading before WC, 285, after, 215. Was also interesting to compare TDS of our filtered water and tap water.
 

fishorama

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See, we told you a TDS meter is both informative & helpful!! Now you know! Your water change #s seem, well, ok, not terrible in any way.

But I'm interested in your tap vs filtered water too. What did you see? My newish fridge is always indicating it would like a new water filter...but that just seems like a sales gimmick. I'm gonna order a new TDS meter soon, next Amazon order.

Don't you feel you have a better idea of TDS & water changing schedule with your new meter? You reduced your TDS by 25% How much water did you change? That's the bottom line...But now you really will know what's happening. You won't have to test all the time once you get a good idea of what happens in your tank & how much water to change to keep it fairly steady.

You've taken a big step forward in being able to understand what the heck is going on in your tank, kudos! It's not a magic answer to every possible problem...but water changes almost always help...They're my first line of defense when deciding my next step. You've got this!
 

tackful

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Last week, tap/filtere was 85/75 TDS. This week, 90/80, possibly because at certain times of year more of our water comes from the Russian River here in California
 

fishorama

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That sounds similar to what my tap tds was as I recall...in the spring after (hopefully) good winter rains. But mine tended to get a lot higher as CA summer dry weather continued. There can be big differences with different water cos. & sources. A friend had a tap tds 230+ higher than mine only 5 miles or so away (different town & water supplier)

Try to get an idea of how much tds tends to go up in a week if that's your WC schedule. You may need to do slight larger or more frequent WCs to keep it "similar". Go slow(ish) with very large tds changes. It used to be called "pH shock", then "osmotic shock" (see "old tank syndrome"). Some do not buy into that theory at all. That really applies more to people who only "top up" evaporation losses...ever. The "Walsted method" with LOTS of plants & very few fish can work, in theory. But while my tanks are lightly stocked now, I know my fish are more active & breed more often with regular water changes.

I admit I got into less than good WCing habits with our loonngg CA drought. I pretend my lotsa plants & poor fertilizing helps make up for that...my husband helps with WCs too but he's a heavier feeder. Find a balance that works for you tank. Juvenile fish will grow & maybe breed; plants grow. Things will change over time & now you have another easy to use tool. Stick it in the tank, press a button, rinse in tap & let dry. No shaking or color comparisons for tds. Dang, I'm putting 1 in my Amazon cart right now!
 

sk8r

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Jun 10, 2023
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Another solution is ro/di---to which you have to add the minerals appropriate for your fish, since ro/di filtration leaves you with pure h2o, nothing else. It is a way to control buildup over time, but you then have to test to track what you may need to add. Ro/di is fairly easy to manage if you have a basement or washroom, but it does involve buckets and pumps and a pretty high ratio of wastewater----I have used ro/di in in marine, and simply route the wastewater to bath or washing machine: it's perfectly good water, just not for fishes.
 
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