TDS comparisons

[glenna]

Well, the tap water has 115 TDS reading and the tanks vary from 150-165.
YIKES
this seems like a big difference to me, but not really sure HOW big of one.
I am wondering HOW big of a water change will be safe under these circumstances. I routinely do 50% or so, and none of the fish have minded so far (they are not big talkers, so it is a little hard !!!)
any thoughts?

[bookpage]

Mine is not as good as yours.

Out of the tap, the TDS is 310. My tanks range from 420 to 550. Hope my meter is off.

[plaalye]

The difference between your tanks & tap doesn't look too bad to me glenna, from 310-550 is a getting in the realm of concern bookpage.
TDS is Total Dissolved Solids so without knowing exactly what these solids are it's all guesswork.
test your gh, kh, nitrates, anything else you have a kit for in order to get a better picture. What are you using for substrate, decor? What are you adding to the tank? Fertilizer, water conditioner, etc.??

I'm not a fan of 50% water changes unless there's a problem. I prefer 2x25%

That's my 2 cents, water chemistry is not my strongpoint so hopefully Diana & Chefkeith will be along.

[chefkeith]

glenna -

I think your tank TDS sounds about right. When fish tank water is +50 ppm greater than the tap water that's probably when you're overdue for water change and filter cleanings.

When my tap TDS is 100 ppm, I try to keep my loach tank TDS in the 125 to 135 range. Currently my tap water TDS is 100 ppm and loach tank water TDS is 130 ppm, while the nitrates are around 10 ppm. If I don't do water changes for a week my TDS will get to about 140 ppm with my nitrates at about 20 ppm. If my TDS gets higher than 150, then I know I'm getting behind on tank maintenance.

In my planted snail tank, I keep the TDS in a 200-220 ppm range. I do add fertilizers to the water and also add some calcium by keeping a bag of crushed coral in the filter. The plants and snails do better with harder nutrient rich water.

You just need to figure out what the optimal TDS range is for the tap water and for the purpose of the tank. For you it might be 150 to 165 ppm.

I agree with plaalye also. I like 2 - 25% water changes better, even if they are back to back, over one 50% water change.

[Diana]

The most sensitive fish I have tried to keep did not even handle a 10% drop in TDS. Most other fish are fine with that much.
Here is how to figure it out:

Tap: 115 TDS
Tank 150 TDS

A 50% water change =
Finished water in the tank comes from:
50 % @ 115
50 % @ 150

.5 x 115 =57.5
.5 x 150 = 75.0

Add: 57.5 + 75 = 132.5

Compare to 10% less of 150 =
150 - 15= 135

A 50% water change is right at the edge of risky. You might want to try 40%:

40% @ 115 = 46
60% @ 150 = 90
46 + 90 = 136
This would be safe.

Then monitor the conditions and if your goal is to always do 50% then do another water change before the TDS hits 150.

_________________________________________________________

Now lets try 2 water changes, back to back. 25% each:

1st water change:
25% tap water @ 115 =28.75
75% tank water @ 150 = 112.5

28.75 + 112.5 = 141
This is not very much of a change. Quite safe.
But does it drop the nitrate and other toxins enough?

2nd water change:
25% tap water @ 115 = 28.75
75% tank water @ 141 = 105.75

28.75 + 105.75 = 134.5
This also drops the tank into the barely safe range. (For really delicate fish- Most of the fish we keep are not this delicate)

[glenna]

Thanks Chefkeith and Diana,
this is VERY helpful and I think I will change my ways based on these calculations.
I think with reduced feeds (makes me sad, but oh well)
and smaller water changes (even back to back) things will be a lot safer.
I (and my fish appreciate it!)

[glenna]

oh, and what's up with your water, Bookpage?
I know that sounds negative, but it is so different from mine and it makes me wonder why. IT is likely not a big issue, if your local water runs that way, then so does the water at the LFS, so the fish are used to it. As long as the water parameters are very similar from tank to tank, the fish should be fine, right?
Still, it seems like you are hobbled coming out of the gate, if your water has high TDS ( I would wonder WHAT is in there). When you buy a fish, do you see a big difference between the bag water, and your own?
Who knows, maybe there are a lot of minerals naturally.
I am still learning so much, that I have immediate reactions that are not necessarily valid.

[starsplitter7]

My TDS is also about 300 out of the tap. It is because of the limestone that Florida is basically made from. I have a tap pH well over 7, but my tanks are in the 6s. I do lots of frequesnt small changes to try not to shock my fish too badly.

[chefkeith]

bookpage- you getting a lot of evaporation? The higher the TDS the more impact evaporation will have.

[Diana]

TDS out of the tap here is barely under 300, often pretty close to 280.
My soft water tanks run to the low 300s, unless I have been just topping off for a long time, then they start creeping up.
GH and KH are pretty stable at about 4-5 degrees = about 90 ppm.
I know the water company adds something to keep the pH up, so I assume most of the rest of the TDS is from this material. About 1 ppm chloramine, too.

[bookpage]

sorry posted twice

[bookpage]

My evaporation is not very much at all (maybe a gallon or two a week) and I change about 25% of water in each tank every week. I'm thinking because of all the plants I have that maybe some of the TDS comes from the dying leaf parts that I can't get out.

[Diana]

Plant fertilizers can add to the TDS, too.

[chefkeith]

bookpage- Dead plant matter shouldn't raise the TDS that much. are you adding fertilizers? What kind of substrate do you have. Something might be leaching.

[chefkeith]

bookpage- Dead plant matter shouldn't raise the TDS that much. are you adding fertilizers? What kind of substrate do you have. Something might be leaching.