ok so here is my question:

my tap water has 10ppm nitrates
so...if i have 40ppm nitrates in my tank, then change 25%, the nitrates get diluted presumably, but by how much?? what is the ratio for working this out??
is it 25% of 10 (2.5) plus 75% of 40 (30) added together?? so it would then be 32.5

So if i were to do a 50% water change it would be 50% of 10 (5.0) plus 50% of 40 (20) = 25?

does that make sense??

i'd just like to know so that i can work out how much water i need to change in order to lessen the nitrates in the tank, and not accidentally keep them basically the same, and eventually building up over time, if you know what i mean??

if my system of calculating is right, then i will do 50% water change every time the nitrates get to around 40 (every 10days or so i have noticed) to ensure that the nitrates are significantly reduced.

thanks

Kat - Your calculations for dilution look good and correctly account for the nitrate concentration in your tap water. Clearly, your fish load determines how soon your nitrate concentration gets up to 40 ppm. One suggestion - if you use fish pellets that contain around 30% crude protein instead of the higher protein food (over 40% protein), your fish will excrete less ammonia. They don't need the extra protein unless you are trying to grow them very quickly.

Dennis

thanks dennis, glad to know my maths isnt too rusty! i feed pellets with high proten as they are babies so i am trying to help their growth. but i keep a close eye on my nitrates and usually change the water when they hit around 40. i will bear my calculations in mind so i know that i am reducing the nitrates significantly, despite the tap waters nitrate level.
thanks again!

I fed heavy rich protein food too~everbody want their babies to grow faster~ ^-^

That is an interesting point Dennis, I've not really thought of that before - although it makes sense Worth considering that along with stocking levels, fish size, filtration and running nitrAte levels - that's got me thinking about it all now! It's interesting because most have of "quality" brands always state very high protein levels as a selling point

A couple of additional points on this. Protein is mostly nitrogen by weight. The function of "food" is to provide energy and to provide building blocks for growth. The protein is important for growth. You don't need protein for energy, however. Carbohydrates to nicely for that, and metabolize to carbon dioxide and water. Protein produces ammonia as a waste product.

If your fish are mature and you are feeding them to provide energy, 30% crude protein food will do nicely and produce 25% less ammonia (just a guesstimate). Do even young fish need the extran 10% protein? I'm not convinced. I do hedge my bets, however and my sweet pea (butterfly koi, keeping my ryukin company) has grown about an inch in the past month.

Dennis

good points. i was always planning on reducing the protein levels of their food when they had grown to about 3-4 inches. my fish are very small at the moment and i have it on no authority that the extra protein is that important, but the foods i am using have been reccomended for encouraging growth (hikari lionhead and tetrafin gold japan) They have 40-50% proteien, which understandably will result in more ammonia, yet because of their size they are fed small portions only, which helps with the amounts of waste produced. (ie less than if you were feeding bigger portions of the same food to a much bigger fish)

I think more important for growth is space, water quality (esp greenwater) alongside a diet rich in all vitamins, minerals, carbs, protein etc etc. (ie good quality pellets, vegetables, algae, and lots of variety!)

Very useful information dennis, thank you.

very good calculation....