Ro Top Up Water - Pure Or With Minerals ?

[nilocmal]

when you add ro water to top up a tank's evaporated water, do you add pure ro, or ro with minerals ?

i've been doing the latter for 5 months, and just noticed my tank's ph has dropped to 7.8 from a steady 8.3 in pre ro days. calcium has also shot up to 480 from a steady 400 in pre ro days.

my fault for being over confident and not testing the water for a while of course. the tank itself seems happy enough, except for a recent outburst of algae - hairy green stuff on the sides and nasty looking red / brown stuff all over the sand on the bottom. hence the recent water test with worrying results.

all other readings seem fine though:
amonia - 0
nitrite - 0
nitrate - 5
sg - 1.022
phosphate - 0

so from now on, pure ro, ro with minerals, something else - what do you reckon guys ? all advice greatly appreciated people.

 

[SkiFletch]

Pure RO. Salt mixes are designed to mix with pure water that does not have solutes/minerals in it. You could be unknowingly playing with your chemistry balance by using the re-mineralized water.

 

[nilocmal]

thing is though, doesn't pure RO have an even lower ph than RO with minerals added, in which case the ph in my tank is going to continue to drop through the floor unless i do something to artificially bring it back up again ?

here's the thing. i converted to marine last summer using de-chlorinated tap water. ph was a steady 8.3 from day 1 onwards. last december i started topping up with RO from the LFS in whose wisdom i trusted that minerals needed adding to the RO for this very purpose. at the same time i stopped testing the water, more fool me. then a few days ago tests show the tank's ph to be 7.8.

surely if i continue down this road, with or without minerals, the tank's ph is eventually going to match that of the RO i'm adding, which will gradually kill everything as i'll haver an acid bath instead of a reef tank ?

if it helps, i've never done a water change per se. all i've been doing is topping up evaporated water, initially with de-chlorinated tap water for the first 6 months, then with mineralised RO water for the last 5 months.

thoroughly confused as ever. what does everybody else here do ?

 

[robbhp]

What you are doing is just topping the tank up. You are only replacing the evaporated water. The only down side to doing this is the fact that only pure water (your salt will not leave your tank nor will anything else) will evaporate. You are then re topping this up with fresh ro water that is of a very low PH, + adding some form of minerals? That are buffering the water a bit but not as much as is need, hence 7.8. What you need to do is get a tub of fresh ro NO SALT or MINERALS, and use this for the top up in the tank (evaporation). All though this will lower the ph a bit it will not do any harm as you only top up with a very small amount every day. You will then need to do a water change every week. I do 10% ( I have a large tank ) if you have a small tank you will want to do more say about 30% would be a great place to start and then drop that down after a couple weeks to say 20% . You will then not have to worry about the PH CAL MAG, as the fresh salt water mix (water change) will top them back up for you. It’s as easy as that. All you have to do is water changes and the tank will be back to normal in a few weeks.

When you add the salt mix, it is more than just salt you are adding. In most good salts you will also add over 70 trace elements that are found in salt water, these are what you are trying to add via the minerals. You are doing the correct thing but just ass about tit. All you need is pure RO to take care of the evaporation and a tub of mixed salt water/RO for the water change, you need to do a water change once a week.

Hope that helps mate ROB

 

[SkiFletch]

Yeah, Rob's right there. You have to do water changes. What's happening is that over time, calcifying organisms in your tank are depleting it of calcium, alkalinity, and magnesium. These 3 elements pretty much govern the pH of the tank. When all 3 are at correct levels, your pH will be around 8.2. However given enough time, things like coraline algae, snails, corals, worms, invertebrates, and other organisms will consume those elements to help them grow. Like Rob said, mixes for marine tanks contain all these minerals that the organisms in your tank are consuming. Thus regular water changes are needed to keep them at a high enough level.

There is one caveat with pH, photosynthesis and respiration. In the morning before the lights come on, your tank will have a low amount of CO2. CO2 is an acid in water, so it tends to lower your pH. However in the morning, the CO2 is low and the pH high. Then, during the daytime, photosynthetic organisms stop taking up CO2 and your fish come out, swim, and produce it. Thus CO2 levels are highest in the evening before lights out. At this point the pH is lowest.

Tanks with poor surface agitation and/or high bioload will experience large swings in pH. I know of a local reefer whose tank is 8.2 in the morning and 7.8 by the end of the day... Yikes. He's just running fish-only though so he can get away with that. Bottom line, I'd suggest you measure your pH in the morning when you wake up, and then again that same day in the evening. If there is very little change, you have good water circulation and good gas exchange. If there is a big swing between lights on and lights off, you'd be well suited with more flowrate.

 

[nilocmal]

many thanks rob and ski. your help and advice is very much appreciated. makes a lot of sense now, which is always half the battle i find in this game.

sounds like proper water changes are the way forward then. i'll give it a go and let you know the outcome.

thanks again guys

 

[SkiFletch]

Anytime. Since you haven't done water changes at all, it might be a good idea to start with one larger change (30-40%) before you maintain with smaller ones. It will take far less time to bring the chemistry back to appropriate levels if you start with a big change.

 

[robbhp]

any time mate, i have taken so much away from this place, thst it is only fair i give it back. if you keep up with those water changes you will find your tank will be loads better in a few weeks. also as ski said a biger water change will help get you on your way as well.

rob

 

[norite]

There is one caveat with pH, photosynthesis and respiration. In the morning before the lights come on, your tank will have a low amount of CO2. CO2 is an acid in water, so it tends to lower your pH. However in the morning, the CO2 is low and the pH high. Then, during the daytime, photosynthetic organisms stop taking up CO2 and your fish come out, swim, and produce it. Thus CO2 levels are highest in the evening before lights out. At this point the pH is lowest.

Um, ski, haven't you got that the wrong way round? At night time, plants take in O2 and give off CO2, therefore in the morning just before the lights come on, CO2 should be highest and therefore the pH is the lowest. Then during the day, plants take in CO2 to photosynthesise and give off O2, so the pH should gradually rise as the day wears on...?

 

[n3ont3tra]

There is one caveat with pH, photosynthesis and respiration. In the morning before the lights come on, your tank will have a low amount of CO2. CO2 is an acid in water, so it tends to lower your pH. However in the morning, the CO2 is low and the pH high. Then, during the daytime, photosynthetic organisms stop taking up CO2 and your fish come out, swim, and produce it. Thus CO2 levels are highest in the evening before lights out. At this point the pH is lowest.

Um, ski, haven't you got that the wrong way round? At night time, plants take in O2 and give off CO2, therefore in the morning just before the lights come on, CO2 should be highest and therefore the pH is the lowest. Then during the day, plants take in CO2 to photosynthesise and give off O2, so the pH should gradually rise as the day wears on...?

I think you're both a little mixed up. The corals and other photosynthetic creatures take in CO2 and put out O2. The fish, however, take in O2 and put out CO2. At night, the photosythetic creatures stop photosynthesizing, but the fish still breathe. So, there's more CO2 in the water, because there's no photosynthesis going on. The pH is lowest in the morning, because there's more CO2, and higher in the afternoon because there's less CO2. So the PH lowers at night and rises during the day.

If you have good surface agitation, it drives off CO2 and brings in oxygen. So that will make your PH more stable (probably).

 

[SkiFletch]

Who me, get it backwards, never

Sorry bout the confusion, n3ont3tra is right about the pH swings and the take home message . More surface agitation = more-stable pH.