DKH unstable

fijiphil · Sep 10, 2018

Hi Randy,
I test parameters every 3 days using Tropic Marin test kits. I dose 3 part Balling salts via a GHL dosing pump controlled by a profilux controller. The Part B is dosed in 24 equal doses (7ml each) over a 24 hour period.
Parts A & C are dosed in the same fashion but on a schedule whereby only one of each part is dosed within 20 minutes of any other.
Calc & Mag remain fairly stable (notwithstanding slight changes which are probably due to testing inconsistencies.)
DKH can rise or drop by anything from 0.3 to 1.1 between 3 day tests , which concerned me. To try to see what was the reason I started testing 3 times a day at 9am, noon and 3pm to see what resulted. The swings are still there and can show 7.5, 7.0 & 7.7 respectively at those times.
Any ideas apart from "Testing Pilot" error?
(The tank with sump is approx 900 gallons with a moderate to light bio load. Rtn flow is 7 times tank volume. Loop flow is the same. Lighting is Orphek LEDs ramping up from 5am to 7am, holding for 8 hours and ramping down from 6pm to 8pm. Auto water change is done 1 gall at a time 45 times a week (equally spaced over the 7 days))
Thanks

reeferfoxx · Sep 11, 2018

What is the dkh of your auto water change system? Also, with that, have you monitored salinity?

chipmunkofdoom2 · Sep 11, 2018

Is this tank really 900 gallons? Or was that a typo? If the tank really is 900 gallons, it's highly unlikely that dosing 7 ml 24x a day is causing that change in your alkalinity.

fijiphil · Sep 11, 2018

"What is the dkh of your auto water change system? Also, with that, have you monitored salinity?"

Hi ReeferfoxMy new saltwater is 7.8 DKH. The testing samples are always taken from the tank overflow box to avoid a recent dose of anything in the sump affecting the tests. Salinity is fairly rock solid between 1.0245 and 1.0255 - checked with a hydrometer and Profilux probe. ( Had a theory that maybe my top off system (RO/DI water at 1.2 DKH) was the cause but I turned it off and still got the swings).

"Is this tank really 900 gallons? Or was that a typo? If the tank really is 900 gallons, it's highly unlikely that dosing 7 ml 24x a day is causing that change in your alkalinity."

Yes Chipmonkofdoom, the tank with sump is 900 gallons and yes, I agree with you hence my seeking advice on other potential causes. I felt it was possibly bad testing but I have had 2 people independently testing. When I compare their readings the swings appear in both tester's readings albeit that their numbers are not exactly the same as each other. It has me baffled...