When to do a water change

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my tank has been up and running now for almost 7 months. I have been doing weekly water changes and my nitrates have been staying around 5ppm and phosphate .03 until about a couple months ago when I started adding corals I added some green star polyps, and a couple of colony's of zoa. Since then my phosphates have dropped down to .01ppm and nitrates are at zero. I have tried feeding more and leaving filters socks in for a week a d even prolonged water changes to every other week. Just recently decided to not do a water change till both were up. It has been almost a month with no water changes with no increase in phosphates or nitrate. I am concerned I may be loosing some needed parameters for my corals and fish. Should do a water change?
Parameter
Salinity .35 ppmNitrate 0 ppm
Phosphate .01 ppm
Calcium 360 ppm
Mg 1380
Ph 8.0
Kh 8.0
 
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SchrutesReefs

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Besides the above mentioned, your calcium looks low, otherwise I would sat you’re doing well for no wc in that amount of time.
Any idea what your cal was before the corals? Looks like you only added soft corals so curious where the calcium went if it was higher before. What salt do you use?
 
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Calcium has always been low always around 340 -360 I am using API test kit to test calcium, I use instant ocean reef crystals. I have not added calcium to raise it as my corals seem to be doing fine and wasn't sure it was nececarry for the soft corals I have.
 

SchrutesReefs

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Calcium has always been low always around 340 -360 I am using API test kit to test calcium, I use instant ocean reef crystals. I have not added calcium to raise it as my corals seem to be doing fine and wasn't sure it was nececarry for the soft corals I have.
I use the same salt but I am using Red Sea test kit for cal. I have a few sps and lps in my tank and my calc sits at 430-440 at 1.025
 

BostonReefer300

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This is a common problem and you're right to be a little concerned about low nutrient levels---both for the health of your corals and for trying to avoid dinos. What tests are you using for NO3 and PO4? You said you're using API for Ca which is OK if you're not keeping corals with hard skeletons, but it's a good idea to move away from all API tests if you can afford to do so because they pretty much all suck. Red Sea, Nyos, Salifert are all better in the simple test category. Hanna checkers are much preferred IMO.
 
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In my experience, nitrates at zero are problematic. The easiest way to goose them up is to add food grade sodium nitrate (I add half a cup of the NAN03 crystals to 1 gallon of RODI to make a stock solution). A teaspoon of stock solution into 100 gallons will give you a measurable low reading of nitrate (Red Sea Pro or Salifert).

Now you can disregard this if you feed quite a bit and have extensive nutrient export in your system (e.g. a big honking skimmer or macroalgae). In that case, the fish poop will feed the corals but the nutrients will get exported before they show up as nitrates.
 
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I don't have nuisance algae in the tank. I do get a brown dusting of algae on the glass and powerheads but takes about a week to show up and I just wipe them clean. I do have a 4.5 gal refugium that has softball size cheato and some green film algae. The cheato has started to crumble since the nutrients dropped and added a trochius snails to eliminate the green algae. I also cut the light back so only running 8 hours now. My skimmer is probably over sized but have it just dry skimming right now so doesn't collect much. My tank is a 75g and a 20 gallon sump. Thinking maybe need more fish have 3 green chromis and 2 clowns thay are about 3" long per fish and my largest clown is about 4". But all fish are youn and I expect them to practically double in size. They have already doubled in size since I got the .
 
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This is a common problem and you're right to be a little concerned about low nutrient levels---both for the health of your corals and for trying to avoid dinos. What tests are you using for NO3 and PO4? You said you're using API for Ca which is OK if you're not keeping corals with hard skeletons, but it's a good idea to move away from all API tests if you can afford to do so because they pretty much all suck. Red Sea, Nyos, Salifert are all better in the simple test category. Hanna checkers are much preferred IMO.
I use API test for nitrates and Hanna for phosphates I will eventually upgrade my test kits but was measuring nitrates before but now it is at zero. Was just hoping to use up what I have before buying a different test kit.
 
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