Reef Chemistry Question of the Day #68 Water Changes and Sump Size

[cope413]

I was just playing around with my sheet a bit and found numbers that may be of interest...

In the question, .25ppm was added to the tank per day. A 1% daily WC gave the Reefkeeper ~24ppm of nitrate at the end of the year.

If we were to change the WC% to 10% monthly, instead of 1% daily, and keep the nitrate addition consistent - you would end up with 51.78ppm at the end of the year. Virtually double. This is interesting because it's 1/3 of the water change volume (10g/month vs. 30g/month).

I'm going to play around a bit with it, and try to put together a sheet that allows you to plug in your desired range for nitrates (or whatever you'd like) and the cost/additive (in this case salt because it's a WC), and find the most cost efficient method to achieve the desired range.

For example, say you wanted your nitrates to be between 20-40ppm. If your salt costs $0.30/g, a 1% daily change in a 100g tank costs you $110/year.
A monthly 20% change would cost you $72/year and still produce the desired result (33.74ppm at the end of the year - within the desired range). A $38 saving.

Shouldn't be difficult to goal seek to come up with a cost saving plan for all supplements/additives...

 

[beaslbob]

Right after I bought a bridge in Brooklyn from Paul_b, I conducted a test of this duplicating everything. At the end of the year I couldn't tell the difference with my api test kit. :squigglemouth:

 

[Randy Holmes-Farley]

Right after I bought a bridge in Brooklyn from Paul_b, I conducted a test of this duplicating everything. At the end of the year I couldn't tell the difference with my api test kit. :squigglemouth:

:lol:

 

[Keithcorals]

I know just enough to find this annoying or possible be annoying but one thing I do know is "equilibrium" would be reached when the amount of nitrate removed by a one percent water change was the same as was added per day. So at some point if your system builds .25 nitrate per day and you change 1% day you would end up with a nitrate level of 25 and once it hit 25 it would stay there as long as .25 a day was added and 1% was removed every day

If you added a bigger sump so the the water change was only .5% you would reach equilibrium at 50ppm

So although a larger sump may prevent excess nutrients from building up faster if the same amount of water is changed it would allow them to build to higher levels. This could be overcome by a large water change at some point but it could also be overcome by simply providing sufficient filtration to prevent the
buildup of nutrients in the first place

If the system goes up .25ppm per day this is what you would get at some point
.5% = 50ppm
1% = 25ppm
2% = 12.5ppm
3%= 8.33ppm
4%= 6.25ppm
5% = 5ppm
Someone better at math than me could tell you how long it would take to get to those numbers

 

[Randy Holmes-Farley]

If you added a bigger sump so the the water change was only .5% you would reach equilibrium at 50ppm

So although a larger sump may prevent excess nutrients from building up faster if the same amount of water is changed it would allow them to build to higher levels. This could be overcome by a large water change at some point but it could also be overcome by simply providing sufficient filtration to prevent the
buildup of nutrients in the first place

The larger sump actually reaches exactly the same final value, it just takes longer to get there.

Here's the day by day for two years:

Day 100 gal sump 200 gal sump

0	0.00	0.00
1	0.25	0.13
2	0.50	0.25
3	0.74	0.37
4	0.99	0.50
5	1.23	0.62
6	1.46	0.74
7	1.70	0.86
8	1.93	0.98
9	2.16	1.10
10	2.39	1.22
11	2.62	1.34
12	2.84	1.46
13	3.06	1.58
14	3.28	1.69
15	3.50	1.81
16	3.71	1.93
17	3.93	2.04
18	4.14	2.16
19	4.35	2.27
20	4.55	2.38
21	4.76	2.50
22	4.96	2.61
23	5.16	2.72
24	5.36	2.83
25	5.55	2.94
26	5.75	3.05
27	5.94	3.16
28	6.13	3.27
29	6.32	3.38
30	6.51	3.49
31	6.69	3.60
32	6.88	3.70
33	7.06	3.81
34	7.24	3.92
35	7.41	4.02
36	7.59	4.13
37	7.76	4.23
38	7.94	4.34
39	8.11	4.44
40	8.28	4.54
41	8.44	4.64
42	8.61	4.75
43	8.77	4.85
44	8.93	4.95
45	9.10	5.05
46	9.25	5.15
47	9.41	5.25
48	9.57	5.35
49	9.72	5.44
50	9.87	5.54
51	10.03	5.64
52	10.18	5.74
53	10.32	5.83
54	10.47	5.93
55	10.62	6.02
56	10.76	6.12
57	10.90	6.21
58	11.04	6.31
59	11.18	6.40
60	11.32	6.49
61	11.46	6.59
62	11.59	6.68
63	11.73	6.77
64	11.86	6.86
65	11.99	6.95
66	12.12	7.04
67	12.25	7.13
68	12.38	7.22
69	12.50	7.31
70	12.63	7.40
71	12.75	7.49
72	12.88	7.57
73	13.00	7.66
74	13.12	7.75
75	13.24	7.83
76	13.35	7.92
77	13.47	8.01
78	13.58	8.09
79	13.70	8.17
80	13.81	8.26
81	13.92	8.34
82	14.03	8.43
83	14.14	8.51
84	14.25	8.59
85	14.36	8.67
86	14.47	8.75
87	14.57	8.84
88	14.68	8.92
89	14.78	9.00
90	14.88	9.08
91	14.98	9.16
92	15.08	9.24
93	15.18	9.31
94	15.28	9.39
95	15.38	9.47
96	15.47	9.55
97	15.57	9.63
98	15.66	9.70
99	15.76	9.78
100	15.85	9.86
101	15.94	9.93
102	16.03	10.01
103	16.12	10.08
104	16.21	10.16
105	16.30	10.23
106	16.38	10.30
107	16.47	10.38
108	16.56	10.45
109	16.64	10.52
110	16.72	10.60
111	16.81	10.67
112	16.89	10.74
113	16.97	10.81
114	17.05	10.88
115	17.13	10.95
116	17.21	11.02
117	17.29	11.09
118	17.36	11.16
119	17.44	11.23
120	17.52	11.30
121	17.59	11.37
122	17.66	11.44
123	17.74	11.50
124	17.81	11.57
125	17.88	11.64
126	17.95	11.71
127	18.02	11.77
128	18.09	11.84
129	18.16	11.90
130	18.23	11.97
131	18.30	12.04
132	18.37	12.10
133	18.43	12.16
134	18.50	12.23
135	18.56	12.29
136	18.63	12.36
137	18.69	12.42
138	18.75	12.48
139	18.82	12.54
140	18.88	12.61
141	18.94	12.67
142	19.00	12.73
143	19.06	12.79
144	19.12	12.85
145	19.18	12.91
146	19.24	12.97
147	19.29	13.03
148	19.35	13.09
149	19.41	13.15
150	19.46	13.21
151	19.52	13.27
152	19.57	13.33
153	19.63	13.39
154	19.68	13.45
155	19.74	13.50
156	19.79	13.56
157	19.84	13.62
158	19.89	13.68
159	19.94	13.73
160	19.99	13.79
161	20.04	13.85
162	20.09	13.90
163	20.14	13.96
164	20.19	14.01
165	20.24	14.07
166	20.29	14.12
167	20.33	14.18
168	20.38	14.23
169	20.43	14.28
170	20.47	14.34
171	20.52	14.39
172	20.56	14.44
173	20.61	14.50
174	20.65	14.55
175	20.69	14.60
176	20.74	14.65
177	20.78	14.71
178	20.82	14.76
179	20.86	14.81
180	20.90	14.86
181	20.95	14.91
182	20.99	14.96
183	21.03	15.01
184	21.07	15.06
185	21.11	15.11
186	21.14	15.16
187	21.18	15.21
188	21.22	15.26
189	21.26	15.31
190	21.30	15.35
191	21.33	15.40
192	21.37	15.45
193	21.41	15.50
194	21.44	15.55
195	21.48	15.59
196	21.51	15.64
197	21.55	15.69
198	21.58	15.73
199	21.62	15.78
200	21.65	15.83
201	21.68	15.87
202	21.72	15.92
203	21.75	15.96
204	21.78	16.01
205	21.81	16.05
206	21.85	16.10
207	21.88	16.14
208	21.91	16.19
209	21.94	16.23
210	21.97	16.27
211	22.00	16.32
212	22.03	16.36
213	22.06	16.40
214	22.09	16.45
215	22.12	16.49
216	22.15	16.53
217	22.18	16.58
218	22.20	16.62
219	22.23	16.66
220	22.26	16.70
221	22.29	16.74
222	22.31	16.78
223	22.34	16.83
224	22.37	16.87
225	22.39	16.91
226	22.42	16.95
227	22.45	16.99
228	22.47	17.03
229	22.50	17.07
230	22.52	17.11
231	22.55	17.15
232	22.57	17.19
233	22.60	17.22
234	22.62	17.26
235	22.64	17.30
236	22.67	17.34
237	22.69	17.38
238	22.71	17.42
239	22.74	17.46
240	22.76	17.49
241	22.78	17.53
242	22.80	17.57
243	22.83	17.60
244	22.85	17.64
245	22.87	17.68
246	22.89	17.72
247	22.91	17.75
248	22.93	17.79
249	22.95	17.82
250	22.97	17.86
251	22.99	17.90
252	23.01	17.93
253	23.03	17.97
254	23.05	18.00
255	23.07	18.04
256	23.09	18.07
257	23.11	18.11
258	23.13	18.14
259	23.15	18.17
260	23.17	18.21
261	23.19	18.24
262	23.20	18.28
263	23.22	18.31
264	23.24	18.34
265	23.26	18.38
266	23.27	18.41
267	23.29	18.44
268	23.31	18.48
269	23.33	18.51
270	23.34	18.54
271	23.36	18.57
272	23.38	18.61
273	23.39	18.64
274	23.41	18.67
275	23.42	18.70
276	23.44	18.73
277	23.46	18.76
278	23.47	18.79
279	23.49	18.83
280	23.50	18.86
281	23.52	18.89
282	23.53	18.92
283	23.55	18.95
284	23.56	18.98
285	23.57	19.01
286	23.59	19.04
287	23.60	19.07
288	23.62	19.10
289	23.63	19.13
290	23.64	19.16
291	23.66	19.19
292	23.67	19.22
293	23.68	19.24
294	23.70	19.27
295	23.71	19.30
296	23.72	19.33
297	23.74	19.36
298	23.75	19.39
299	23.76	19.41
300	23.77	19.44
301	23.79	19.47
302	23.80	19.50
303	23.81	19.53
304	23.82	19.55
305	23.83	19.58
306	23.85	19.61
307	23.86	19.63
308	23.87	19.66
309	23.88	19.69
310	23.89	19.71
311	23.90	19.74
312	23.91	19.77
313	23.92	19.79
314	23.93	19.82
315	23.95	19.85
316	23.96	19.87
317	23.97	19.90
318	23.98	19.92
319	23.99	19.95
320	24.00	19.97
321	24.01	20.00
322	24.02	20.02
323	24.03	20.05
324	24.04	20.07
325	24.05	20.10
326	24.06	20.12
327	24.07	20.15
328	24.07	20.17
329	24.08	20.19
330	24.09	20.22
331	24.10	20.24
332	24.11	20.27
333	24.12	20.29
334	24.13	20.31
335	24.14	20.34
336	24.15	20.36
337	24.15	20.38
338	24.16	20.41
339	24.17	20.43
340	24.18	20.45
341	24.19	20.48
342	24.20	20.50
343	24.20	20.52
344	24.21	20.54
345	24.22	20.56
346	24.23	20.59
347	24.24	20.61
348	24.24	20.63
349	24.25	20.65
350	24.26	20.67
351	24.27	20.70
352	24.27	20.72
353	24.28	20.74
354	24.29	20.76
355	24.29	20.78
356	24.30	20.80
357	24.31	20.82
358	24.32	20.84
359	24.32	20.87
360	24.33	20.89
361	24.34	20.91
362	24.34	20.93
363	24.35	20.95
364	24.36	20.97
365	24.36	20.99
366	24.37	21.01
367	24.37	21.03
368	24.38	21.05
369	24.39	21.07
370	24.39	21.09
371	24.40	21.11
372	24.41	21.13
373	24.41	21.15
374	24.42	21.16
375	24.42	21.18
376	24.43	21.20
377	24.43	21.22
378	24.44	21.24
379	24.45	21.26
380	24.45	21.28
381	24.46	21.30
382	24.46	21.32
383	24.47	21.33
384	24.47	21.35
385	24.48	21.37
386	24.48	21.39
387	24.49	21.41
388	24.49	21.42
389	24.50	21.44
390	24.50	21.46
391	24.51	21.48
392	24.51	21.50
393	24.52	21.51
394	24.52	21.53
395	24.53	21.55
396	24.53	21.57
397	24.54	21.58
398	24.54	21.60
399	24.55	21.62
400	24.55	21.63
401	24.56	21.65
402	24.56	21.67
403	24.56	21.68
404	24.57	21.70
405	24.57	21.72
406	24.58	21.73
407	24.58	21.75
408	24.59	21.77
409	24.59	21.78
410	24.59	21.80
411	24.60	21.81
412	24.60	21.83
413	24.61	21.85
414	24.61	21.86
415	24.61	21.88
416	24.62	21.89
417	24.62	21.91
418	24.63	21.92
419	24.63	21.94
420	24.63	21.95
421	24.64	21.97
422	24.64	21.99
423	24.64	22.00
424	24.65	22.02
425	24.65	22.03
426	24.65	22.04
427	24.66	22.06
428	24.66	22.07
429	24.66	22.09
430	24.67	22.10
431	24.67	22.12
432	24.67	22.13
433	24.68	22.15
434	24.68	22.16
435	24.68	22.18
436	24.69	22.19
437	24.69	22.20
438	24.69	22.22
439	24.70	22.23
440	24.70	22.25
441	24.70	22.26
442	24.71	22.27
443	24.71	22.29
444	24.71	22.30
445	24.71	22.31
446	24.72	22.33
447	24.72	22.34
448	24.72	22.35
449	24.73	22.37
450	24.73	22.38
451	24.73	22.39
452	24.73	22.41
453	24.74	22.42
454	24.74	22.43
455	24.74	22.44
456	24.74	22.46
457	24.75	22.47
458	24.75	22.48
459	24.75	22.50
460	24.75	22.51
461	24.76	22.52
462	24.76	22.53
463	24.76	22.55
464	24.76	22.56
465	24.77	22.57
466	24.77	22.58
467	24.77	22.59
468	24.77	22.61
469	24.78	22.62
470	24.78	22.63
471	24.78	22.64
472	24.78	22.65
473	24.78	22.67
474	24.79	22.68
475	24.79	22.69
476	24.79	22.70
477	24.79	22.71
478	24.80	22.72
479	24.80	22.73
480	24.80	22.75
481	24.80	22.76
482	24.80	22.77
483	24.81	22.78
484	24.81	22.79
485	24.81	22.80
486	24.81	22.81
487	24.81	22.82
488	24.81	22.83
489	24.82	22.85
490	24.82	22.86
491	24.82	22.87
492	24.82	22.88
493	24.82	22.89
494	24.83	22.90
495	24.83	22.91
496	24.83	22.92
497	24.83	22.93
498	24.83	22.94
499	24.83	22.95
500	24.84	22.96
501	24.84	22.97
502	24.84	22.98
503	24.84	22.99
504	24.84	23.00
505	24.84	23.01
506	24.85	23.02
507	24.85	23.03
508	24.85	23.04
509	24.85	23.05
510	24.85	23.06
511	24.85	23.07
512	24.85	23.08
513	24.86	23.09
514	24.86	23.10
515	24.86	23.11
516	24.86	23.12
517	24.86	23.13
518	24.86	23.14
519	24.86	23.15
520	24.87	23.16
521	24.87	23.16
522	24.87	23.17
523	24.87	23.18
524	24.87	23.19
525	24.87	23.20
526	24.87	23.21
527	24.87	23.22
528	24.88	23.23
529	24.88	23.24
530	24.88	23.25
531	24.88	23.25
532	24.88	23.26
533	24.88	23.27
534	24.88	23.28
535	24.88	23.29
536	24.89	23.30
537	24.89	23.31
538	24.89	23.31
539	24.89	23.32
540	24.89	23.33
541	24.89	23.34
542	24.89	23.35
543	24.89	23.36
544	24.89	23.36
545	24.90	23.37
546	24.90	23.38
547	24.90	23.39
548	24.90	23.40
549	24.90	23.40
550	24.90	23.41
551	24.90	23.42
552	24.90	23.43
553	24.90	23.44
554	24.90	23.44
555	24.91	23.45
556	24.91	23.46
557	24.91	23.47
558	24.91	23.48
559	24.91	23.48
560	24.91	23.49
561	24.91	23.50
562	24.91	23.51
563	24.91	23.51
564	24.91	23.52
565	24.91	23.53
566	24.92	23.54
567	24.92	23.54
568	24.92	23.55
569	24.92	23.56
570	24.92	23.56
571	24.92	23.57
572	24.92	23.58
573	24.92	23.59
574	24.92	23.59
575	24.92	23.60
576	24.92	23.61
577	24.92	23.61
578	24.92	23.62
579	24.93	23.63
580	24.93	23.63
581	24.93	23.64
582	24.93	23.65
583	24.93	23.65
584	24.93	23.66
585	24.93	23.67
586	24.93	23.67
587	24.93	23.68
588	24.93	23.69
589	24.93	23.69
590	24.93	23.70
591	24.93	23.71
592	24.93	23.71
593	24.94	23.72
594	24.94	23.73
595	24.94	23.73
596	24.94	23.74
597	24.94	23.75
598	24.94	23.75
599	24.94	23.76
600	24.94	23.76
601	24.94	23.77
602	24.94	23.78
603	24.94	23.78
604	24.94	23.79
605	24.94	23.80
606	24.94	23.80
607	24.94	23.81
608	24.94	23.81
609	24.95	23.82
610	24.95	23.83
611	24.95	23.83
612	24.95	23.84
613	24.95	23.84
614	24.95	23.85
615	24.95	23.85
616	24.95	23.86
617	24.95	23.87
618	24.95	23.87
619	24.95	23.88
620	24.95	23.88
621	24.95	23.89
622	24.95	23.89
623	24.95	23.90
624	24.95	23.90
625	24.95	23.91
626	24.95	23.92
627	24.95	23.92
628	24.95	23.93
629	24.96	23.93
630	24.96	23.94
631	24.96	23.94
632	24.96	23.95
633	24.96	23.95
634	24.96	23.96
635	24.96	23.96
636	24.96	23.97
637	24.96	23.97
638	24.96	23.98
639	24.96	23.98
640	24.96	23.99
641	24.96	23.99
642	24.96	24.00
643	24.96	24.00
644	24.96	24.01
645	24.96	24.01
646	24.96	24.02
647	24.96	24.02
648	24.96	24.03
649	24.96	24.03
650	24.96	24.04
651	24.96	24.04
652	24.96	24.05
653	24.96	24.05
654	24.97	24.06
655	24.97	24.06
656	24.97	24.07
657	24.97	24.07
658	24.97	24.08
659	24.97	24.08
660	24.97	24.09
661	24.97	24.09
662	24.97	24.09
663	24.97	24.10
664	24.97	24.10
665	24.97	24.11
666	24.97	24.11
667	24.97	24.12
668	24.97	24.12
669	24.97	24.13
670	24.97	24.13
671	24.97	24.13
672	24.97	24.14
673	24.97	24.14
674	24.97	24.15
675	24.97	24.15
676	24.97	24.16
677	24.97	24.16
678	24.97	24.16
679	24.97	24.17
680	24.97	24.17
681	24.97	24.18
682	24.97	24.18
683	24.97	24.19
684	24.97	24.19
685	24.97	24.19
686	24.97	24.20
687	24.97	24.20
688	24.98	24.21
689	24.98	24.21
690	24.98	24.21
691	24.98	24.22
692	24.98	24.22
693	24.98	24.22
694	24.98	24.23
695	24.98	24.23
696	24.98	24.24
697	24.98	24.24
698	24.98	24.24
699	24.98	24.25
700	24.98	24.25
701	24.98	24.26
702	24.98	24.26
703	24.98	24.26
704	24.98	24.27
705	24.98	24.27
706	24.98	24.27
707	24.98	24.28
708	24.98	24.28
709	24.98	24.28
710	24.98	24.29
711	24.98	24.29
712	24.98	24.30
713	24.98	24.30
714	24.98	24.30
715	24.98	24.31
716	24.98	24.31
717	24.98	24.31
718	24.98	24.32
719	24.98	24.32
720	24.98	24.32
721	24.98	24.33
722	24.98	24.33
723	24.98	24.33
724	24.98	24.34
725	24.98	24.34
726	24.98	24.34
727	24.98	24.35
728	24.98	24.35
729	24.98	24.35

 

[beaslbob]

I know just enough to find this annoying or possible be annoying but one thing I do know is "equilibrium" would be reached when the amount of nitrate removed by a one percent water change was the same as was added per day. So at some point if your system builds .25 nitrate per day and you change 1% day you would end up with a nitrate level of 25 and once it hit 25 it would stay there as long as .25 a day was added and 1% was removed every day

If you added a bigger sump so the the water change was only .5% you would reach equilibrium at 50ppm

So although a larger sump may prevent excess nutrients from building up faster if the same amount of water is changed it would allow them to build to higher levels. This could be overcome by a large water change at some point but it could also be overcome by simply providing sufficient filtration to prevent the
buildup of nutrients in the first place

If the system goes up .25ppm per day this is what you would get at some point
.5% = 50ppm
1% = 25ppm
2% = 12.5ppm
3%= 8.33ppm
4%= 6.25ppm
5% = 5ppm
Someone better at math than me could tell you how long it would take to get to those numbers

(if I understand you correctly) That's what I thought----at first. But nothing has changed in the system. the same bioload and therefore the same amount of nitrates being generated in twice the water. So now the daily build up in only .125ppm/day. But the 1g water change is now 1/200 so the steady state=.125ppm/day/(1/200)=.25 Betcha people thought I was joking with the average of e and g is F. But with 1/2 the daily build up in ppm and 1/2 the daily water change they end point remains the same.

 

[Keithcorals]

(if I understand you correctly) That's what I thought----at first. But nothing has changed in the system. the same bioload and therefore the same amount of nitrates being generated in twice the water. So now the daily build up in only .125ppm/day. But the 1g water change is now 1/200 so the steady state=.125ppm/day/(1/200)=.25 Betcha people thought I was joking with the average of e and g is F. But with 1/2 the daily build up in ppm and 1/2 the daily water change they end point remains the same.

The end point isn't the same. The 1% water change will never let the nitrates get past 25 and the 5% will let it go until 50. But this is more of a math problem than anything that will every happen in reality. If the timeline went to 3-4 years it would show up better but they will both be 25 at some point but then the 1% water change will stop and the .5% will continue going up

 

[Randy Holmes-Farley]

The end point isn't the same. The 1% water change will never let the nitrates get past 25 and the 5% will let it go until 50. But this is more of a math problem than anything that will every happen in reality. If the timeline went to 3-4 years it would show up better but they will both be 25 at some point but then the 1% water change will stop and the .5% will continue going up

Sorry, you are wrong. The endpoint is the same for the reason we discussed earlier in the thread:

Now, let's look at a larger sump that doubles the total water volume.

Don't forget that the total nitrate input is the same, so we have only 0.125 ppm per day since the water volume doubled. The multiplying factor in the spread sheet is now 0.995 because you are only changing 0.5%, not 1% of the water volume each day. Eventually this tank must also reach 25 ppm, but it takes a lot longer to get there. At one year you are at 20.97 ppm. Two years you are at 24.33, same as the smaller sump at 1 year.

If you don't believe that, you can run the spreadsheet to 12 years, and it is still approaching 25 ppm, at 24.9999999 ppm.

 

[Keithcorals]

You're right I wasn't diluting the amount of nitrate just the percentage of the water change my math only applies to the first setup with the .25ppm day added not the second with .125 that's what I get for trying to do math thanks for pointing that out

So in a nut shell the more water volume the slower nutrient buildup happens and larger water changes are not required with the added volume only with added nutrients

The same thing applies to the uptake of trace elements but in reverse twice the water would cut the rate of depletion in half. This was why I has asked you about low ph causing alk to drop I'm considering adding a large container to my system just for stability but wasn't sure if it would also cause a need for the addition of more alk or at least not sure to what extent it would effect it.

 

[Randy Holmes-Farley]

The same thing applies to the uptake of trace elements but in reverse twice the water would cut the rate of depletion in half. This was why I has asked you about low ph causing alk to drop I'm considering adding a large container to my system just for stability but wasn't sure if it would also cause a need for the addition of more alk or at least not sure to what extent it would effect it.

Yes, that's right. The only drawback I can come up for a larger sump is that it could leak more heat to the room, needing more electricity to keep it warmed in a case like mine where the sump is in a cool basement.